I have a hodge-podge of sleeping arrangements depending on the situation!
I have a PW Plateau - similar bedding arrangement as the Great West.
I usually put 2 king size fitted sheets over the bed - a t-shirt knit one (kinda like a mattress pad) and a regular one. Both my sheets are reject sheets that my mom no longer needs - mostly the elastic is no good anymore on both and I don't really need the elastic in the RV. I Put the sheet over the back of the couch before I lower it which holds it on and I pull up the cushions on the ottomans and put the sheets under and put them back so the sheet isn't going anywhere! When it's cold I have a fleece sheet I use in place of the top sheet.
I have a 0* rated backpacking sleeping bag (mummy style) that I use when it's cold - although I still find that I have to pile on the the layers of long underwear and socks and put blankets over it...that van gets cold, cold, cold. This is an easy option because as soon as the sheets are on I throw the sleeping bag down and I'm ready for bed.
On a weekend trip that is fine, however when I travel for a few weeks in the summer I get to where I can't stand sleeping in the sleeping bag so I make up the bed "normal". I have a top sheet, it's only "double" size, but it's enough. I tuck it in on one side and leave it open on the other. I then throw an afghan I crocheted over that and I have a "twin" size comforter that I throw over that if I need it.
I find that I'm much more comfortable to leave the bed down all the time. This presents a few problems.
1) No table, no place to eat... - Solution: Use the picnic table in the campground, or if there's no picnic table I have a "TV" tray that I stash behind the driver seat that I use - I swivel the passenger seat and sit there.
2) no place to sit and watch TV or relax other than in bed. Solution - sit in the campsite in a camp chair or at the picnic table & read or blog. When I'm at Wal-Mart or a rest stop this is a bigger problem...so I've made a large floor pillow that I use as a backrest and makes part of my bed like a chair.
I'm in a slightly different situation b/c I'm a solo RVer...I just have me to worry about!
Good luck! I hope my experiences can be helpful!