We put a mattress pad on top of the mattress, then cover that with a 2" foam pad. The foam pad is covered with a fitted sheet and then (sometimes) a flat sheet over that. Finally we use camp style sleeping bags as comforters. Sometimes the bags are used as covers, but if it is fairly cold outside, we use them as individual bags.
I know it seems like a lot, but our bed is pretty darn comfy... Oh yeah, we also have about 150 lb of dog heat thrown into the mix...
We use regular fitted bed sheets. We also leave the bed made up when we fold in the bed ends. The trick is as you fold the mattress you need to be fast, yes you need to straighten the top comforter but that is all. We traveled last summer and moved just about everyday without any issues.
We plan on travelling to Canada in June and fitted sheets will be the way to go, since we'll be stopping each night along the way (I only like to drive 8 hours/day). Making the beds from scratch every evening is one way to tick off the wife fast.
Congrats on the 17Z, we love ours! On each bed we use a mattress pad, a fitted sheet, and sleeping bags. The beds fold up fine with the pads and sheets on the mattresses. We also bring a few extra blankets, rolled up and stored in the small space above the beds.
Sheets, comforter, foam pad, the works. One of us inside, and one outside, makes the beds up quick. We take it apart when closing up the bunk doors, since I felt the strain on the hinges was a bit much.