: Thank you Mike,
: I sanded and coated once... Looks much better already! BTW, for the
: sake of any future builders the Rustoleum professional flat
: black has limestone in the formula and I think might be the
: culprit in the cracking finish.
: Cheers!

Flat black is part of the problem here, can't reflect any of the sun's rays and will heat up more than any other color. UV and heat are causing the paint to break down.

Bill H.