sorry brian, but i wouldn’t call grp a heat resistant material.
on the contrary, it stores heat in a semi combustable way if in direct contact with a heat scource.i’ve seen many a reliant robin and scimitar burn truly well, lol.
i am not an alarmist in any way, and last year completed a grp model with two steam engines fitted myself, as have many others ,
but all that is needed in a plastic or grp hull, are, as have been said, wooden barers and fress air………..great idea is to put in small computor power box cooling fans.small, in obtrusive and punch out a lot of cool air.