IF you decide to do this - my recommendations:
(edit to add.. car should be completely functional as to tire tread, exhaust, wipers, horn, no obscured windows, all external lights working and at least one spare in the trunk for every external light, as well as the knowledge on how to install them - or prepare to pay someone to do it if one fails on the trip.)
1. Purchase a document folder that clips, straps, or velcros to the passenger visor of the vehicle. Should be available at any auto parts store. (In a bind, a heavy envelope, preverably with string enclosures, oa zippered pouch can be tied to visor with shoelace, string, or taped to it.)
2. Into that visor go the vehicle's registration, proof of insurance, inspection sticker reciept, tag reciept, letter of authorization to use if the vehicle is titled to someone else, AND the driver's (and any co-driver or passenger's - NO EXCEPTIONS!!!) drivers licenses - ALONG with photocopies of ALL of the above - (you can photocopy more than one item to a page if small enough, & use both sides to keep the item count down - I have even known of some people who "lost" a license, and then later found it, and kept one in the wallet, and the other in the envelope...YMMV...).
3. Clear OUT the glove box, preferable the one in between the seats, if available. Procure some innocuous container, (tampon box, small purse, but DEFINATELY NOT a Crown Royal Bag, or anything else a law enforcement officer can claim to have reason to look into!!!!)
4. Procure medium to small handgun (larger if you can swing it & want to...) to fit inside the innocent container.
5. Guess where the pistol goes?
6. Procure windbreaker, jacket, hoodie, etc with pockets big enough to hold innocent container AND small tape or digital voice recorder, or cell phone that does the same.
7. If the girl leaves the vehicle for any reason, windbreaker goes on, and innocent container goes into pocket. Concealed means concealed. Billfold goes in to same pocket. voice recorder goes some where (under small towel, maybe?) unobtrusive and where it can be started by touch at the first sign of being pulled over.)
8. If the vehicle is stopped, no reason to reach for wallet OR OPEN ANY GLOVE BOX!! Turn on voice recorder and dome light if at night, clearly state time and place and "being pulled over by flashing (color) lights on (vehicle description), turn off vehicle, roll down window, and place both hands either at the op of the steering wheel or out the window, open and facing up if possible. Police are trained to watch the hands - that's what kills you. We don't want him nervous or ill at ease for any reason.
When he does the "License, registration, id of passengers" bit keep you hands still and calmly and politely reply, "I hvae all of that in a pouch on my visor, officer. How would you like me to proceed?" Follow his directions, if lawful, and probably even if they aren't.
9. IF ever asked "Do You Mind/May I/ I want to...search your vehicle", remember the David Spade comercials - "THE ANSWER'S ALWAYS NO!!". NEVER EVER EVER. Not without a warrant, and ask him for one if he persists. If he can legally search WITHOUT a warrant, trust me, he wont ask.... read up on "terry frisk", and KMOW what it means...
10. This part sucks, and takes some research. You will have to find out how long a law enforcement officer in each state may detain a person without probable cause or arresting them. Ideally, this will be by having letters from each state's attorney's office in reply to your letter to them that you intend to visit their fair state and need to know the answer to that question. If the officer says "I don't have a warrant, but I'll keep you right here until I get one." the proper reply is "According to the letter your state's attorney wrote me, you can only detain me for XX minutes without arresting me. You have YY minutes left before I leave whether you like it or not." NO OTHER TALKING! Not where you came from, where you are headed, isn't the weather nice = SAY NOTHING! You don't have to, and they can't use what you don't say against you.
I am not a lawyer, and assume no responsability for the potential adverse consequences of doing this. A familiarity with the legal doctrine of "necessity" is recommended. In my experience, most stattes except the worst selectively enforce gun laws. Young minority guys will get popped every time, old folks and proper young ladies almost never. Most cops have mothers, sisters girlfriends, etc. The big plan is to NOT have an enncounter by NOT giving them a reason to stop you. Make sure you have the cruise control set @ 2 MPH below ALL the speed limits, even the urban and construction zones, and don't tailgate, change lanes frequently, drive eraatically or when sleepy, or anything else that draws attentioin to you.
Better tried by twelve than carried by six.