Robert, I have only heard of one case where the pressure got high enough to blow covering off. Looking at your Pitts I would say you have enough " leaks " to keep from that happening. As far as heat goes I wouldn't worry too much about that either. The IMAC guys flying composite airplanes and canisters and just burying the canisters in the fuse without anything separating the radio gear from the exhaust system. I have had a couple wood and foam 40% airplanes with open motor boxes as well without issue. Those were Monokote covered and the covering you plan to use will stick to the airframe much better.