Anything is possible, of course, but adding the large wall openings you are thinking about will be much more involved on a Boler
13 than on your stick-built camper pictured.
This is because it's more of a monocoque structure - it gets some of its strength just from the shape and continuity of the outer shell.
Secondarily, it gets strength from the built in closet, and, to a lesser extent, from the kitchen counter/brace/upper cabinets on the other side. And also from the windows
Somewhat counterintuitively, the shell is actually very floppy once you remove the windows
Fiberglass is nearly infinitely changeable, but what you are suggesting would be a "big" involved job.
Notice how in your stick-built camper, you frame in the openings? Now think about doing that on something rounded. You could shape the framing pieces, or mold them of fiberglass, but it is not going to be a quick/easy project, in my opinion. I'm presuming you basically just want a hot dog stand, not a long drawn out labor of love.