you have to be able to get a lot of air in ,well you do with gas and I wouldn't have thought spirit would be different, you also have to get the heat out or you will start to have problems with bending and with some glues, this is the reason some people go for open boats as well as being able to see the moving parts, I see the floor of the bridge is grating is it possible to remove the under side of it as that would enable a lot of hot air to escape with doors and windows open. they do create a lot of heat when enclosed I also line the inside of the superstructure with a heat reflective tape they use in motorsport, you will of realised by now how hot it gets from tests but 30 min on a hot day with a big burner produces wood bending heat.
Proteus