We have used common ordinary foam for our permanently set up bed in the rear. Unspecified density, and this kind gradually loses its shape over the years, resulting in bodies hitting bottom and being uncomfortable. The available area is approx. 55" wide and 86" long.
In planning for the eventual replacement we priced foam. Yikes!
By chance we hit on something we'll consider when the time comes. We had to buy a sofa bed for a spare bedroom and went to IKEA and found a setup called BEDDINGE (these Swedes are so cute). Nifty enough sofa, and it can be had with 4 different qualities of 4"+ thick mattresses. The mattresses are all 55" wide by 78" long. The old foam pieces are of standard 72" length, so the extra 6" means that I no longer need to "cool my heels." Hmmmmm........
The mattresses are available from $100 to $240, with the most expensive one being composed of many little coil springs in separate cloth chambers. For our purposes this innerspring one was appropriate. As an afterthought I noticed the dimensions and decided to try it in the trailer. It fit, but had to be squeezed in because of the rounded corners in the Burro
. It turned out to be very comfortable for both Kathy and myself. I had assumed that it would not be, because it is just over 4" thick, but I was wrong. It was very comfortable for me and Kathy.
I briefly checked the construction by opening up the zippered , machine washable cover and found that it would likely be no big thing to modify two of the corners for a more relaxed fit.
They can be furnished with several types of covers and colors, but the thing that caught my attention was that because they are meant for a sofa bed they are actually two separate mattresses with a cloth hinge (which can be cut with a scissors). They are of unequal width but that makes no difference in this application.
Because it can be split into two, installation and removal is very easy. This mattress appears to be of pretty high quality and durability, so when the time comes this will likely be our solution.