How to make up corner beds

I have an Itasca Spirit 25B. I knew the corner bed would be a chore but it turned out to be impossible to make up in the conventional way because in order to claim a "true full size" mattress they used every millimeter of space leaving not even enough space for my fingers to fit between the mattress and the walls. I could tuck nothing in no matter how much I crawled around. So I got 2 adult size fleece sleeping bags/sacks from LLBean. They zip together to make a full size sack and cover the mattress perfectly. There is plenty of friction between the fleece and the mattress cover to keep the bottom sac in place so there is no bunching. I am very happy with it and add a quilt over top as required. It is very easy to pull and replace so I never hesitate to launder it.
This totally solved the problem for me and I love the compact design of my Itasca.