I saw videos of Styromax (another Oz company) building joints like that, and like Victorian mentioned, thought "no way in hell is that a strong joint!" The strength is in the skins and the glue contact skin-skin is very little.
But... if you make a completely torsion free subframe and reinforce edges with internal structure, and use the right glue, then it apparently works! Seems a bit crazy to me, but the proof is always in the result.
Couldn't you make any angle you wish using that method? With CNC it should be easy. Also, what glue did you use?
I used Sikaflex 252 (along with the appropriate cleaner and primer). Others are probably just as good.
The use of aluminium corner reinforcements requires a consideration of differential expansion between the aluminium and the FRP skins and that effects the thickness of the glue joint. That is not required if the corner reinforcements are hand laid up or are FRP extrusions.
I suggest that closed cell polyurethane foam is superior to EPS both structurally and in terms of its insulation qualities.
Some urethane foams are "drilled" with 1mm holes allowing resin to create tiny pillars joining the outer skins when it is vacuum bagged wet-on-wet. This creates a panel that is far superior to that made by simply gluing pre-made skins to sheets of foam. The skins are also typically thinner and lighter with no risk of delamination.
This is a camper made by a friend.
The sandwich panel was made wet on wet and vacuum bagged on his shed floor (14 years ago). The corners are all hand formed and laid. The foam is closed cell polyurethane. The floor is glued to rubber pads which are in turn glued to the chassis direct. There is no steel sub frame. The body is stiffer than the chassis. The outer is painted with 2 pack paint after completion. All the interior "furniture" is also sandwich panel and part of the structure.
Despite appearances it is actually a Defender.
His effort, skill and finish puts mine to shame.

Cheers,
Peter
OKA196 motorhome