My winter projects started with the goal of lowering the car's weight and fixing a fuel starving problem I was having at anything less than a full tank of gas. The solution was a small 4 gal fuel cell. Installing the cell is a pretty major undertaking, and the first step was to clean the paint off the floor of the car where I was going to cut and weld. Since this car has had no interior for most of the last 10yrs, and the interior has been painted at least 3 times without proper prep work, I decided to go ahead and restore the whole interior at the same time. I blame a lot of this on lil buddy's project - seeing all the work he was putting into restoring his car inspired me. Plus mine is a completely rust free southern car that just needed to be cleaned and painted. After I got the interior prepped, my roll cage welds started to bother me. I built the cage at least 10 yrs ago, and I couldn't weld that good back then, plus all I had was a 110V mig. While I had it all clean I went ahead and TIG'd all of the welds again to make them look better and be stronger.
Now for the picture version of the story:
Start with a pile of overpriced plumbing and a 4gal aluminum fuel cell.
Cut a hole in the floor and weld in a frame to hold it in place.
Go ahead and strip the rest of the interior down since you're in there anyway.