I always get rid of the factory mattress and put in a good residential one. I also size down to ease the effort of having to put sheets on. Most of the time the mattress is completely flush with the side walls and just a hassle to put sheets on. I have an adjustable Sleep Number at home, and to get my correct angle in the 5th wheel, I put two layers of 2 inch styrofoam under the top third of the mattress and it works like a charm. Here's to good sleeping....
2012 Dodge 3500 Cummins Crew Cab 4X4, "Decluttered" and Tuned/2013 Forrest River Viper XLR 390V10 Toy Hauler/2012 Harley Davidson Ultra Glide CVO.
Full time RVer.