The thick paper should protect from indirect heating on the balsa really well. It can also be lightly sprayed with water if you want to increase the effectiveness. If you're worried about head conduction through the cabanes into the balsa then you can clamp a large metal clamp or pair of pliers onto the cabane strut just before it enters the balsa; It'll act as a heat sink and, although won't prevent the heat from conducting down to the wood it will at least give you more time before it reaches the point at which you need to start worrying.

Cheers,
Neil.