The best way I have found to bend mild steel is to score a line down the bend line with a cut off disk on the angle grinder. Just thin the metal a little along the line that you want to bend. Then you can pretty much bend it by hand or just sandwich it in the vise between a couple of pieces of angle iron so that the bend line it just above the angle iron and bend it over. Then finish off with a hammer to tighten the bend up. Finally I run a weld bead down the inside just to strengthen it.
I've done all my battery boxes that way and it works fine.
My battery box design for the front (click for bigger ver):
Hole in the tub.I cut about an inch of the cross member out so the box can sit above the torsion bar and a little further forward and there's no need to put a step in the bottom of the box, it basically sits just above the torsion bar:
Side view of box without sides:
Test fitting in the tub (sides not on yet):
You can use any number of battery hold downs. I weld a rod to the lower front of the box for the lip on the battery to sit under and use the stock Fiero battery hold down rubber block screwed into a nut welded underneath the box. Basically the same setup as the stock Fiero battery hold down.
I actually mount the battery facing forwards with the terminals passing through a couple of holes cut in the front of the box. I 'line' the holes with a 1/4 inch or so sliver of PVC pipe glued in place and put a piece of plastic sheet or something glued to the front of the box to avoid shorts when installing the battery.
I also install a battery cutoff switch on the front cross member so that I can disconnect the battery easily without having to fumble around the front trying to undo screws.
This setup lets the spare sit in pretty much the stock location.
[This message has been edited by ltlfrari (edited 11-18-2009).]