I searched the *marts far and wide and none of them in my area carried the eggshell, so I broke down and bought a double-wide extra thick self inflating mattress over the web (ThermaRest brand).  Was expensive, but I could sleep all night without having arms and legs falling asleep.

We put it under the queen bed in our 2720 and deflated it (by lying on top of the mattress) before folding the trailer.  This worked fine.

Since then I realized I should have searched the local fabric stores, too, for the eggshell.   My preference would put it under the mattress.