My grandson that age will sleep on the couch, dinette lowered to a bed, or if he is really tired, he will just sack out on the floor anywhere. Last visit, I put him on the floor on a self inflating mattress, he loved it.
We used a PackNPlay for a long time, but he started resisting it at 18 months, and it is a real problem getting him into one before he is asleep. Simply recoginises it for the prison that it is.
His mom just found him something called a PeaPod, kind of a small mesh tent. He loves it, but we are not sure how it is going to work. Says "Mommy night night" to get her to put it up for him, but doesn't always go to sleep when in it.
Grand-daughters (twins) started RVing with us age 3. Slept together in dinette until too big, then together on sofa. Bedtime, tney would go down when told, talk and play until asleep. But that's twins.
Small children can, and do, sleep anywhere, any time they are ready to sleep. So RVing, or tent camping, it is a matter of your goals. Are you trying to find them a place to sleep, are are you trying to find a place to confine them for the night. If confinement is the goal, PackNPlay can sometimes work to age 3-4 depending on size and agility, but I don't expect toddlers to go happily into their prison cell while awake.