Does that buggy have the .25 force engine? If it does, you wont be able to keep the temps under 300 and still make good power because they use garbage material in their engine manufacturing, why do you think they are so cheap. You probably cant get it started after it dies either huh, they have a bad hot start problem because the fuel boils in the crankcase and carb. All you can do is like you said, seal it up with air seal you buy from the lhs all around the carb and maybe try using a less percentage of nitro. I had the .25 force engine and it ran hot all the time and lost compression after 2 gallons of 20% running rich too, in my opinion the .25 engines suck and they are a ripoff but I hope you have better luck than I did. Dont mean to rip on your buggy just telling it like it is.