Ok, the solution would appear to be an extensible, elevate-able, twin
bed that - with the extension, can hold a "full/double" mattress and
with the foundation parts added, can be lofted to the required height.
Since the idea of transporting the completed work is a design
consideration, the idea of a bed constructed of suitable sub-
assemblies would seem to work out nicely.
If the Long Twin Mattress is the same length as the "Full/Double" that
would be the way to go. Ooops, should have said "design for the length
of the two mattresses to be employed." Or should that be "deployed?"
Now, that would be a creation worth a patent or two, no?
If you go that far, call it the "Tarballs College Bedding Solution"
and send me a picture!