I've just passed level 8 without exploiting the fire bug in part D. B)
I used 2 blockers, 1 builder and 1 miner in A,
1 builder in B,
2 floaters in C
and 2 bombers, 2 bashers, 1 miner and 2 diggers in D.
Saved: 71% with about 2 seconds left.
Cool level! On to level 9 . . .