With 36R tires, I almost always run Yokomo Firm inserts. Especially in the hotter temps. Our track gets up to 165deg F, in the summer time. In the hot temps, you definately want some air gap. It seems like this helps keep the tire from overheating.
TLR, Spektrum, Tekin, SMC, MO-GRIP, www.factory-rc.com https://www.shapeways.com/shops/MPP