The Phoenix Cruiser B+ cap is not an upper bunk by default, but can be ordered to be a small one for a child or for bulk storage as pictured in this old 15 year old PC. A new PC would look somewhat different, but this gives you an idea on what to expect. I would request that large finished board be avoided to get max room up inside.
Here is a picture early in the manufacturing process showing the size and insulation of an open B+ cap. Note the van roof has been cut away for easy entry from the house, and to open up the interior. With an upper bunk, I would make certain they do NOT cut the roof to maintain best roll-over protection.
PCs are designed for cold weather camping. The walls, floor, and ceiling are well insulated. Here is a cut-away of the floor. Note the steel beam and durable protective under-belly plastic shielding.
Thermal pane windows are optional. Ordering a PC without an optional slide out will be much warmer than one with a slide out. All PCs come with interior heat-protected plumbing and fresh water tank. The exterior waste tanks are insulated and have large 12V heating pads, similar to that used for heated seats.
Our PC-2350 has no slide out and has double pane insulated glass. The only cold of significance we deal with comes from the Ford cab area. We drape an old comforter across the two front seats and tuck it around the outer edges to eliminate low-drafts. It would be easy to completely seal the front cab from the house if we had an upper bunk as pictured above because the van roof would not be cut-away, creating a clean vertical surface to seal well with a comforter from the bunk to the floor.
