Re: "The Bat Tank"
I think the bat is a great idea. The problem is in what you're referring to as 'welding'. Aluminum is much different from other metals, so you can't silver solder it, for example. There is a stuff called alumarod (Ithink that's what it's called) which you can use with a propane torch. It is imperative when using this stuff to prepare the surfaces with a stainless steel wire brush (usually comes with the rods) as something like steel wool or a steel wire wheel will contaminate the area you're trying to join and it simply will not bond. I have little experience with this, but it might work. If you google aluminum welding rods you'll find a lot more information on this and some video stuff that makes it look easy as pie. Maybe it is. Hopefully it is.
If you wanted to go another route, if you had everything ready (cut off to the length you want, a piece of aluminum to cap the end already made up, holes drilled where you want the cap to go and petcock, someone who does that work professionally and has the equipment could do that up in a small amount of time I would think. Then you know you have a really good weld you don't have to worry about leaking. I don't know how thick those bats are, probably pretty good, but once you cut it off and look at it you can decide if you want to build up the filler opening and petcock opening a bit to give more metal for cutting threads. Something to think about is the spot where the fill cap will go. Would that need to be offset somehow since the sides are tapered and right where it would be best to have it located you have a top cross bar in the way? Something to think about. Also how to mount it. Leather straps would work. More stuff to get creative with. The shape and quality of an aluminum bat is a compelling starting point. Somebody else here will know more than I do and maybe point you in the right direction. I hope you do it. The more options we have, the better... in motors, transmissions, sprockets, mounts and gas tanks. Different applications and different budgets.
Someday when I grow up I will probably lose interest in toys with wheels, but until then...