Store ammo, clips, guns all seperately. I moved from New Orleans to Phoenix using a 26ft uhaul. I actually wrapped the longarms in moving blankets and packet them in the gunsafe, the pistols were boxed and also went in the gun safe. the gunsafe went in the uhaul 2nd, right next to the refrigerator in the front. I had no problems, and never go pulled over. I did play it safe and carried the ammo out on the next trip when I drove my truck out. I know you may not be able to do it like this. I would dis-assemble the weapons you can, and pack them in the uhaul and put the ammo and clips in the SUV. This would probably be better for the ammo and powder because it wont be going through warn, cold, warm transition, and will be at a more constant temp....unless you stop for the night.
now that I think about it, you might even want to reverse that, just incase something happens to the trailer, your guns will not be lost, powder and ammo and clips can be more easily replaced. just my .02 cents worth.