How to bond wall and roof panels together

[cineview]

Im going to use 40mm sandwich panels, but want to have both sides covered with gelcoat so that no foam from the core is visible, at the same time get the best strenght as possible.
Any smart way to cut this to make it fit like this?

[QueticoBill]

Is "sandwich panel" ply-foam-ply with no other framing between ply skins? And then fiber glass and epoxy or other resin on inside and outside?
Just let outer ply on walks extend to top of roof.

[cineview]

On the top of my head, im thinking something like this.
Where it says skin, its excessive gelcoat/fibreglass skinm enough to cover the exposed foam core in the roof and floor panel. There i will add extra sealing, enough to make sure there never will be a leak.
Thoughts?

Heres also a picture of the panels im going to use, xps core with fibreglass/gelcoat skin, 40mm
The panels will also be inserted with a square alu profile for each running metre of the panels.