Have you brought up the idea of having them use the tent for sleeping and 'all' their clothes? Most kids would really go for the idea - having their own private space for late-night chatter and sleeping late in the morning.
If they won't go for that idea I'd suggest laying down some ground rules beforehand - like they won't be able to sleep late since you'll be up earlier. You can't walk around them sleeping in that small area. Have them carry their bedding back & forth to the tent during the day. It will take up sitting room in your RV. None of their clothes, makeup, etc. can be scattered in the RV if you plan for the tent to be their dressing room. They should also help with some cooking or dish chores otherwise it will not be a vacation for any of you. Have them plan some things to do during the days so they can't complain of 'not wanting to do that'.
I think it could work out well and be glad she still wants to go with you! Have fun..
