For the sofa--have you used an "egg crate" mattress cover? If you get a king size one, you can cut it to size (if necessary). When not in use, fold it tightly and bungie it with two bungies to keep it small. It should store under the sofa. We haven't slept in it yet, and we don't use an egg crate--but we did with another RV we had.
Thanks for the idea of the props under the center of the sofa bed!
We bought ours last October to use as a second car in addition to an RV. We get a lot of snow here so we haven't used it much. We're down to our last one foot on the ground---now we should be able to use it more.