Super custom high top childrens upper bed boards

Hi there all I’m a newbie and have luckily upgraded to super custom from a Regius which I loved but am very happy to be a new super c owner.

A quick one if it’s ok to ask some advice…
I have seen a few with the storage above drivers cab area with kids bed boards that go accross and you can sleep 2 small children up top.

This van has the space but not the boards or side fittings.

Would anyone know how best and of course safely without damaging the side walls or mounts much to do this safely??

my 2001 KZH138V has it's hood lining glued to roof....so I can readily see the "rails" which run from front to back where a low roof would sit on top...I can't see an issue with screwing off to the rail to fix a new rail to support bed boards...perhaps use nutserts in case there is wiring behind that run through the "rail" tube (so avoid sharp self tappers which could damage wiring) what year do you have?... mine has aircon unit which would need removing to make that project work

Thank you for your wisdom Geoffrey yes good idea re inserts