(12/31/2001):  Last mod for 2001!  First the 'story'...  It was the morning of my first set of finals (college) -- I get up, eat, etc.  Its freezing outside, and I get out to the bug and try to start it.  (Insert annoying 'battery dead' cranking noise here).  For some reason the battery was dead.  I don't live that far away from school so I could've walked no problem - but having a dead battery was annoying.  I didn't feel like walking (I was lazy) so I turned the ignition on and put the car in neutral and pushed it backwards out of its parking spot.  After I got as far as I could push (its on a little hill) I pushed it forward and jumped in it and put it in gear and popped the clutch and started it (what a mouthful).  Of to school I went.  After the finals I got back in the car, and to my surprise it actually started!  So I thought that maybe something just drained the battery...  The next morning I had finals 'round 2'.  The battery was dead again.  According to all my gauges the charging circuit was fine, so later (the next weekend) I tested the battery - it couldn't hold a charge.  It was a 5 year old AutoZone battery (it was installed THE DAY I bought the car).  I figured it was time to replace it and 'upgrade'.  I bought an Optima 'red top' as the replacement.  Its an expensive battery, but its one of the only ones that is a dry cell, vibration proof, battery that can be mounted upside down, doesn't spill any acid, and doesn't emit hydrogen gas.  This battery is rated at 750 cold cranking amps, my old one was rated at something like 560 or so.  It also had a good warranty on it.  The optima was physically a little bigger (taller) than the previous battery; it still fit, but I didn't have a way to mount it.  I have always been paranoid about the springs from the bottom of the rear seat arcing across the + and - posts of the battery and starting a fire (I've heard too many horror stories about this) so I thought it might not be a bad idea to install a battery box. 

Since I was at college (away from home/tools/etc) I temporarily just let the battery sit under the back seat (its so HEAVY it didn't really move around)...  As an extra precaution I also taped a grease rag over the + terminal just to be safe for the trip home.

You can see part of the 'original' battery mount in the pic below - it just a simple clamp, but it doesn't quite work on a lot of newer/larger batteries.

I went to wal-mart to find a battery box, but they were out, so I went to pep-boys.  Below is the smallest one they had.  Its a little tall but the battery fits very good inside. It also wasn't very expensive at $11.  (Oh as a side note - if you get one of these Optima batteries KEEP the plastic handle!  it comes in VERY hand if you ever need to take the battery out, or move it around - Its HEAVY!).

Despite the way this picture looks, the battery does fit well inside the box.  It was too tall however, so after I measured it, I took the dremel to it, and chopped off about 1" off the top (I also had to remove the 'handles' on the side, so that the lid would fit).

To mount it I just used a couple strips of galvanized metal (to spread the load) and sheet metal screws (its quick and dirty but it works).  I made sure to coat the screws with RTV so it wouldn't let any moisture in.  Before I put the top on, I cleaned the connections and coated them in silicon dielectric compound.  The box is kind of a pain to get to fit, but with a little grunt work it DOES go in.  Mine ended up coming a little to close to the rear seat rail, and the strap on the battery box was going to rub against it - to keep it from eating into the strap I cut a piece of thick fabric (actually, the stuff I used to cover the springs when I reupholstered the seats) and slid it between the rail and strap.

All in all it worked out pretty good... Not the most 'smooth' installation ever, but good enough.  Now I don't have to worry about my new battery sliding around, or shorting out.