Folks, the fed law pertains to altering the vehicle to make a hidden compartment. Adding a firearm safe which is cable locked under your truck seat or putting your pistol into the glove box is not a violation + fulfills the locked up requirement (which usually reads 'inaccessible').
This was taught to me in a law enforcement training course years ago and again in the 2000's in a drug interdiction course. Personally, i agree that it is Stupid- you own the vehicle and in my America, you can alter it however you want to. But that isnt going to change the law's existence. And again, i dont recall how this applies to motorhomes. It doesnt apply to TTs, 5ers, or truck bed campers, just the vehicles that we think of as passenger vehicles.
(and like many laws on the books, i have never heard of a non-criminal ever being charged under this law)