Having built 2 for myself and a flying buddy ,i had the same problem with my first , i cannot find any paint that will stand the heat [&o],the P80 outer is just too close regardless of any gap and coats of BVM HP paint ! ,I stripped my b/pass back to edge of the turbine body
and used matt black exhaust paint ,leaving the gloss on the rest.
I know how you feel i watched mine bubble up after the first run[:'(]