(January 25, 2016 at 8:31 am)SteelCurtain Wrote: You need to use softer wood then. Sugar pine tends to have straight grain, and won't warp when you cut it. If you have a lumber yard near, they'll usually finish two edges (S2S) with a jointer/radial saw so you can work off of those edges.
(January 25, 2016 at 8:32 am)SteelCurtain Wrote: Poplar is also cheap(ish) and easy to work with.
Are they strong woods?, tank will be around 500kg when filled.