Building your Perky is a good chance to learn how to make your own tank.
Fashion a wood block the size of your tank out of pine or some such soft wood, then wrap sheet metal around it. Brass shim stock, .010" is what I always use. The Perky is a good "tank trainer" since it doesn't need to stunt or go inverted.
You get four sides with one continous wrap, the add the two end plugs.
The third picture shows a tank form being sawed to size & shape. The dowel was inserted 'cause I was chicken to get my fingers in the buzz saw.