Mattress questions for 2027 Cascadia

I started to learn about beds a year ago. Before I had been sleeping on whatever was in the truck, but since I'm going back to living on the highway I thought I'd get the best I could. Have a few questions about the interior fitting:

The bottom bunk is 42" wide for the basic configuration correct? Has anyone here put a twin xl on the 42" bunk? 4" of extra unfilled space seems like a lot.

I'll be in the raised roof with the folding top bunk which will be folded up. How tall of a mattress can I really put in there? Looking at a 14" model.

How much storage space would I lose by having trouble lifting the bed tray? Also I don't care about being able to use the little pull out shelf. I care most about sleeping as good as possible.

Thanks in advance!