If the temperature is over 70°F and I plan to ride for more than a mile, I will usually be riding without a shirt. That eliminates outside the waistband carry for concealment. Inside the waistband at the side is impractical while riding a bicycle because of the constant leg movement. Even if I lost the extra 35 lbs around my waist, appendix carry would be difficult because of the forward lean while I ride, and appendix carry makes me nervous. Inside the waistband at the rear would also be exposed. Also, it would take too long to pull a pistol out of my panniers. A holster mounted on the bicycle frame might be possible, but hiding it may be difficult, not to mention the vibration issues. The only practical solution would appear to be a fanny pack holster, provided that I can make it look geeky enough that nobody would expect me to be carrying a pistol inside it. I ride a bicycle with panniers on both front and rear and with full fenders and 2.25" wide tires. So while riding on my bicycle a fanny pack would not seem at all out of place. I haven't found anything to my liking at any local gun shops or online. So I decided to make a fanny pack holster for my Sig P365X. This is a proof of concept prototype. Meaning that I needed to make a fanny pack holster prototype that I can use to see if I can realistically and reliably draw a firearm and backup magazines. If it works I can make refinements later. I used the Sig holster that came with my P365. FYI, this holster is now obsolete and Sig makes a similar holster that fits both the P365 and the P365XL. This fanny pack is designed to also hold the new XL compatible holster. I glued one end of the trigger guard retention bolt to the holster so that it could be adjusted with only one Allen wrench. I used JB Weld Plastic Bonder, which is a 2 part urethane adhesive. I cut off the normal belt clip mounting points from the holster. To clear the magazine button extension, I cut a slit into the holster, softened it with with heat gun and then bent it and held it in place until it cooled. I glued the holster to a couple of sheets of aluminum to achieve the necessary spacing. I used JB Weld Epoxy to hold the aluminum sheets together. I used JB weld Plastic Bonder, to hold the plastic holster to the aluminum mounting plates. I drilled 3 mounting holes in the aluminum plates. I may add a few safety wires across the holster, just in case the glue breaks loose, but I don't really think they will be necessary. With the limited tools that I have at my disposal, I chose to use a rectangular aluminum extrusion for the internal frame to hold the holster and magazine carriers. The extrusion is 1/8" thick with external dimensions of 1.75" x 5.00" and internal dimensions of 1.50" by 4.75". The extrusion is way too thick and too heavy. But I first need to know if I can even draw from a fanny pack at the rear and this appears to be the easiest material to use for the prototype. My first attempt was with a cardboard mockup that was 11" long. It seemed like it might work and would be able to hold 3 additional magazines. But after I mounted the holster on the aluminum extrusion and belted it around my waist, it became immediately apparent that the end of the pistol was just too far outward for my arm to move even further outward far enough to be able to draw the pistol from the holster behind my back. Fortunately I bought extra extrusion for more than one try. This time I reduced the extrusion length to 7.50" long. It would only be able to hold 2 extra magazines. I modified the extrusion and mounted the holster to it. I belted it around my waist behind my back and lo and behold I was able to draw from the holster relatively easily. The next step was to make a form to simulate the magazine shape so that I could bend hot ABS sheet around it. I cut down a piece of 1.5" by 1.5" poplar to nearly the required size and then sanded it to the exact size and shape needed. I used 0.060" thick ABS sheet because I had it, it's easy to form, and I do not yet have any experience with Kydex. I may try using Kydex sheet in the future. I used a heat gun to soften the ABS sheet and bent it around the form into a U shape. It took about 3 tries before I had a usable shape. I did some careful trimming of the U-shaped ABS and glued on the back using a solvent based ABS plumbing glue. I made a second carrier tube the same way. I glued a spacer onto the side of each magazine carrier. Then I glued the carriers to a couple of ABS mounting straps. I cut out a notch on the front and rear of the aluminum extrusion for access to the magazine bases. Then I mounted the magazine carrier to the extrusion with screws. After some experimentation I determined that I needed to cut a round notch from each side of the magazine carrier tubes to be able to better grab the base of the magazines with my forefinger and thumb. The magazine carriers grip the magazines almost too well. I did some sanding to the inside of one of the magazine carriers to make it slightly easier to withdraw the magazine. The first carrier tubes that I made had dimples that pressed into the cutouts that are used for the magazine catch. It held the magazine well, but I noticed that the edges of the hole were sharp enough that they were shaving the ABS when the magazine was inserted and withdrawn. The subsequent magazine carriers were made smooth without the dimples in them. The magazines are held in place by friction. You need to shake the carriers vigoursly before the magazines will fall out. An alternative magazine catch mechanism might be to use a spring loaded ball bearing that rests in the magazine catch hole. I may try that down the road. The aluminum extrusion isn't quite tall enough for the P365X with the MagGuts modified magazine. So I removed part of the bottom of the extrusion and glued on some poplar to effectively extend the bottom of the extrusion. I used Devcon 2 Ton Epoxy to hold the 2 lays of poplar together and JB Weld Epoxy to hold the poplar to the aluminum frame. I did not want the barrel end of the gun rubbing against the aluminum frame while holstering, so I glued an ABS pad to the frame with JB Weld Plastic Bonder. As I mentioned, the aluminum extrusion is too heavy, weighing in at 15 oz. So I did some weight relieving by drilling many holes into it. I reduced the extrusion's weight by 6 oz reducing it to 9 oz. It wasn't really worth the time and effort, but I was already watching the Kyle Rittenhouse trial livestream all week long, so I wasn't really wasting any time. I realize that I still need to make one hole in the aluminum frame large enough to slip an Allen wrench through so that I can adjust the trigger guard retention bolt. I did not want to use an extremely stiff gun belt to hold the holster in place. But I don't need to. When I reach into the holster frame, it contacts the web between my thumb and forefinger and all that I need do is to squeeze my last 3 fingers on the handgrip of the pistol and it pulls the pistol from the trigger guard retainer in the holster. Similarly, when I grab the base of a magazine with my thumb and forefinger, I can brace the rest of my fingers against the frame to extract the magazine from it's carrier tube. The fanny pack does not need to be held in place on the belt nor does the belt need to be stiff. The total weight of the aluminum frame, with the ABS pad and the poplar extension on the bottom, is 11 oz. I could probably reduce the weight by using 0.060" thick aluminum sheet, or possibly Kydex with some aluminum supports, and I may try that on the next iteration. So far the total weight, with the P365X loaded at 14 + 1, plus two 14 rd magazines, is 3 lbs 5 oz. That's also a total of 43 rounds. If I want to get a bit crazy, I could mount additional magazine carrier tubes vertically on the outside of the frame and could easily add two more magazines. This frame may not be ideal, but it appears to be working well enough that it's time for the second phase, which is to sew a rain resistant cover over the frame to make it look like a fanny pack. I plan to have a flap opening on each side held in place with velcro. I will probably add padding to the flaps to round out it out so that it looks more like a real fanny pack. I will have a pouch on the rear that can actually hold something small. It will have a big flap over the top, again held down with velcro. I may embroider some bicycle sounding name to the fanny pack so that it looks more like a legitimate dorky looking old man's or bicycle geek's fanny pack. For now I'm using a 1.5" wide "tactical belt" that I bought on Amazon for ten bucks. I don't think that it is anywhere near stiff enough for use with a regular holster, but it should work well enough for this "fanny pack" design. This is not going to be as fast to draw as a holster at my hip, but I think that it's the best compromise that will work under the conditions for which I will use it. If you have any suggestions for improvements, let's hear them. Especially if any of you have any suggestions for working with Kydex.