There is a discussion of "Comfy Reading Seating...
" at the Casita Travel Trailer Forum (Don't know if you have to join to view, but it is worth joining anyway & they seem to tolerate me as an Escape owner.)
One of the solutions that is expensive, but interesting is the West Marine High-Back Go Anywhere Seat
. Like any marine item it is a bit over priced, but it sure looks like it would be comfortable sitting in place of the bottom cushion in my 17!.