Nice looking battery holder. Well, I would weld it. The gas tank isnt right under it is it? If so then how would you through bolt it? And as far as the removability thing goes, you prolly wont remove it unless your are replacing the pan then its some major work anyway.
So why do I like the weld in method? Cause I dont like screws poking down through to the underside. Just my personal thang. But... If you use stainless screws, say 1/4" and blue locktite the nut and zip saw off the extra threads then thats a really clean look too. I wouldnt use rivets, not a good fastener for a heavy battery. It will wiggle while driving. JR
Ooops, just like Manny said. I like his plan too..