Thank you Mr. Poly Whore,
Hm, i don't know how make nice under body like Robban or others, but i know one thing, i make how i can and i don't give a damn fuck how it looks, because it's a part of car and you don't show it in show of your rides, (image unavailable in archive)
Now re-making under body, and got this so far, (image unavailable in archive)

More Boolen, Extrude are coming.