Sorry Dad! Being the parent of a boy and a girl, and now a 5-time grandparent, take it from someone who has "been there... done that!"... and actually still "doing it" since our adult son is living with us again with his 3 year old son too.... Face it... 3 year olds just can't be confined!
To save your sanity, let the kids sleep in your bed and then once asleep, move them to their bed. They are little only once. And once they are grown, you never get those precious moments back. Let them be little as long as they can be.
Yea, you have no privacy. But ... eventually they DO go to sleep! Start earlier in the evening and if necessary, get them up earlier in the morning.
Also, when it comes to camping, in the camper ... especially at THAT age, they are SO excited! Face it ... they never sleep!
Even an accordion style door will not sound proof their sleeping quarters. The 3 year old will still figure out how to open it, still taunt the 2 year old, and still want to keep the conversation going with you, to avoid sleep and to not miss anything, This is just the nature of a 3 year old.
Don't worry, when they are 13, you won't be able to install ENOUGH door! And all they'll do is slam it, yelling ... "I hate you!" And then you'll wonder what happened to that little angel, so innocently popping their head out from behind that curtain, saying, "HI Mommie! HI Daddy! HI sister! Hi! HI! HI!"
No doors will sound proof in a camper. No doors will keep a 3 year old contained. The curtain is the best. They don't panic behind curtains. Closed door and 3 year old' go nuts! Spare yourself the agony! Keep the curtain.
I know ... been there, done that ... 7 times now!