I would take safes and guns in same trip, or Id get a metal locking box - ie cabinet with a big padlock, whatever completely obscures whats in it that also a cop cant break without special tools, and Id lock them in it for the trip and would refuse to open it under any condition outside of a warrant.
If I only owned a car Id rent a van or uhaul, trailer, whatever, lock that too. Big difference between having access to guns and having them locked up, and a big difference in what police can do, even if you were breaking the law which you arent, when they have no permission or potential access/sight.
I guess Id also add simple things to avoid trouble, make sure lights and vehicle is all appearing tip top, stop at stop signs and dont cut it close on traffic lights, turn signals, speed of traffic or no more than 5 over, dont be high beaming - basically drive nice.
You're covering all the bases here but this post is a bit paranoid. Heck Ive gotten complacent to the point I rarely even follow FOPA anymore. In the 10 or so times I've been pulled over on interstates I've not ever been once asked if I have firearms and have only been issued one citation.