Yes, I've done it. The information you got above is correct. It isn't hard to do, it doesn't take long. About the only hints I can give you, other than the one above about using a tank that already has some damage to it, is to take a grinder to the thing (80 grit wheel) and get all the paint off of its sides and leave good deep scratches before you start banging on it. This will help the heaps of bondo you are going to have to use something to cling to. Also, for your initial buildup, make sure you use a fiber-reinforced filler. Keep your layers of filler relatively thin, about an eighth of an inch at most. That means be prepared to put on a number of coats. Don't cheat by adding additional hardener to speed up the process either, that only weakens the material and decreases the ability to bond.
Normally when you do body work on bare metal you would clean and grind the metal and then seal it with epoxy before going on to your filler. However in this case you are going to have to use an extraordinary amount of filler. This is one of the very few places where you should go straight to filler after you grind (and reclean - use acetone) the metal. Shoot your sealer on after you have done your rough shaping of the filler, not until you're ready to shoot your 2K and start block sanding it. Of course if its going to set for over a couple of days you need to go ahead and seal it.
Back to process. You can do your banging with a plastic or rubber mallet, you can do it with a ball-peen hammer if you like. The one thing is that if you're going to hammer the dents rather than cut and weld them just make sure to take it easy. You can use a big hammer and do the dents in 15 minutes and spend the next three days trying to smooth it out. You can also use a small hammer and lighter blows with it and take 30 minutes to do the job and then spend a half a day to sand it into shape. Your choice.
