What's your height/weight to hide that sucker? I'm thinking about going SP101, but reallt like the idea of the GP100...just not sure if I can hide it.
I design and make my own holsters -- as Sam1911 said, "Wear your pants a size larger, get a good gun belt and holster, and put on an outer shirt or vest. It will be invisible enough for almost all situations." Add a good tuckable design to that, and that GP100 will simply disappear.
I like a holster with a full leather back -- I put the gun on the leather, and draw a line completely around it, about 1 1/2" margin and cut that out. A similar piece is cut for the lower half (trigger guard forward) and stitched to the back, then the gun is inserted and the holster is moulded with rubbing alcohol.
The full leather back (which should be sweat proofed with Sno Seal) protects your skin from the gun, and the gun from your sweat and body oils.
I attach two stiff straps -- either Kydex or heavy leather -- to the toe of the holster with Chicago screws. Belt loops are attached to the other end of the straps.
To wear the holster, you start fully dressed, shirt tucked in, belt unbuckled. The holster is shoved between pants and shirt, and the belt loops are fastened around your belt. Control your gig line and pull your shirt out from behind the holster and drape it over the gun and holster. Tuck it in between the straps and the holster.
Position your gun with one hand and tighten and buckle your belt with the other. When you have everything as you want it, "blouse" your shirt -- pull out a couple of inches all around and let it hang down over your belt.