Here are some details about the upper ("Penthouse") bed. We love the panoramic view and (potentially) cross-breeze when sleeping on this bed. Two people can sleep upstairs if they aren't too large and don't mind being cozy.
The upstairs sleeping area is 54" wide — about the same as a "full" size mattress, but the padded mattress itself is only 39.5" wide — the size of a "twin" size mattress. The unpadded area beyond the mattress works fine as extra room for elbows and heads on pillows (if you sleep with your head towards the rear of the van). Here are my measurements (penthouse bed viewed from above):
We use a set of "twin" size sheets. These sheets have been customized a bit for easier setup — we sewed the bottom of the fitted sheet to the bottom of the top sheet. This also helps the foot region of the sheets not come untucked at night.
Sportsmobile's penthouse mattress is 2.75" thick, of which 1" is wood — leaving only 1.75" padding. This results in a bed that is a bit too firm for us, so we supplement with a foam mattress topper. We purchased a "twin" size foam pad, and cut it into two pieces to match the Sportsmobile's split mattress sections.
The bed hangs from the ceiling when not in use. There is more room (an extra 1.5") above the front mattress section because those two rectangular penthouse roof support pieces don't hit it like they do for the rear mattress section. (See the white padded rectangle with a metal handle on the roof in the photos below.) We remove for storage our rear foam pad section when the van's top is down (it prevents the roof from closing completely), but find we can leave the other piece in place. Here's what the front mattress section looks like with the top up & down: