krobbe wrote:
If there is 5 inches of space beyond the RV short queen mattress(60"x75"), then a standard queen(60"x80") will fit just fine. That is what I did for my TT. I also replaced the supporting 3/8" plywood with a 5" longer piece but didn't really have to. To improve your situation even more, Place a bollard or piece of foam in front of the mattress(under the pillows) to extend the length even more if you have room.
I was going to suggest this. I have an East/West bed in a slide out that actually required a short mattress to fit when the slide is in but the manufacture did give a foam piece that matched the height of the mattress so that once the slide was out the mattress could be pulled down a bit and the foam block placed at the head under where the pillows go to make it full length. Just have to remember to take the foam block back out and slide the mattress all the way onto the bed platform before bringing the slide back in.
I didn't like the mattress that came with the RV so I bought a memory foam mattress from amazon and just cut off the bottom to make it fit the shorter size needed to bring in the slide, then add the cutoff to the top under the pillows when I want the full length. The foot end hangs over the bed platform about 5 inches but only holds my feet so it's not noticeable when sleeping on it. If you do this you might be able to even make a longer option work for you, assuming you need the space when a slide is used. If you have the room you may just do as above and throw the full size mattress on the platform and be done. Then you can look for other options that you might like about a trailer if the bed size can be fixed.