I use something called a tuck shrinker to shrink edges, some people like to use an an edge shrinker, but hammering a tuck more effectively shrinks than a mechanical shrinker. Stretching the center is done with a hammer and shotbag. Lots of people new to metalworking are under the impression that the english wheel is the workhorse of the shop, but most of the shaping is actually done with the first two tools. The wheel is really a finishing and fine shaping tool.
I'm using a wooden buck I made years ago for this tank, since then I usually make a foam buck because it's not really necessary to have something as sturdy as wood when you're just using it as a shape reference. Wood is certainly nice when you need to clamp panels in really complex shapes or where really critical accuracy is required, but for most alloy tanks, getting things within half an inch or so is perfectly fine.