My female lab will be six next month and she has done this from trip one. She was one when we got her and she was a born camper. Biggest issue was when we had the FW and would do an overnighter, next morning was a chore to get her out of the FW and into the truck.
I can touch any key in the house and she is fine but jiggle the MH keys and game on. Doesn't matter if it is a two day or two week trip when we get home we park the MH, unload, go inside and leave her in the MH with the door open. Usually about three hours later she will come crawling through the doggie door with the most pitiful face, look at us and then put herself to bed.