I could be wrong, but I don't beleive heat build up will be much of a problem, especially if you were to use (as you suggested) some well placed and designed heat sinks. I would venture to guess that as the reaction is induced by a spark that heat alone isn't going to be able transfer the ionization energy needed(Ionization energy is simply the energy required to start the reaction or more precisely the energy required to remove the most loosely held electron on the propane). So I personally don't think it is something to really worry too much about.
