I scored a tank extension off of Ebay for $25.00+ shipping. It basically matches the shape of the tank, but still requires a bit of massaging once it's tack welded on.
After measuring and re-measuring (10 times), I tacked welded the center portion and started the afore mentioned "massaging". It's at this point that I decided to allow the
extension to take a rounded slope vs following the tank straight down. I didn't want the end of the tank to sit higher than the front edge of the seat.
Lower is better as the seat can sit slightly above the tank.
Basically, the next step was to press and tack all the way around. Then I went back and filled in any spaces I skipped.
*** Word of caution: Our tanks are not very thick. It's easy enough to burn all the way through (trust me). On the inside, I simply bent and shaped the edges
around using welding pliers so it looks natural.
Once it's welded all the way around, I ground all of the welds smooth so there were no high spots. Hard parts are done...
With a thin layer of filler, I built it up to blend the original shape of the tank with the shape of the new extension.
Once all of the prep work is done, a few good coats of primer and it looks like it's always been there.
Not an easy project. Probably 18-20 hours total and a 5 on a scale of 1-10. But, not really that bad for a home project. Really, the hardest part was stripping the tank to bare metal.
Next step is to test fit it and see how much a seat will have to be reworked to match up to it.