I've seen some THs (5er's and TT's) that decked out the garage really comfortable. Throw down a carpet (if one is not provided with the camper), set up a table with a lamp, hang a television, and the kids will love it! If the kids are going to be sleeping there, get their opinion how they feel. Take them to look at some at the dealer lots, and ask them what they would do to make that space more comfortable for them. What needs to be added, what needs to be changed.
I think you'll be surprised what the kids have to say! When I was a kid, I would have loved to have a room in a camper that was more of an industrial feel than a grandma's bedroom feel any day! (Now I'm married to a grandma and don't have much choice! :) )