The baffle fabrication is easy, the problem is the attachment, especially in the poly tank.

The baffles must resist the torque of the mixer and also must be sufficiently rigid that they don't vibrate excessively in the fluctuating flow of the mixer. The eight-foot tank needs four baffles, eight inches wide and about the length of the tank straight side. Metal baffles 1/4 or 5/16 inch thick and attached at two points to the side of the tank are probably sufficient.

The four-foot poly tank needs four baffles, four inches wide and the length of the side wall. Since attaching metal (or even poly) baffles to the side of the tank is probably impractical, a metal baffle "cage" is probably the best option. Metal baffles 1/4 inch thick can be attached at the top and bottom of the baffles to a ring (slightly smaller than the inside diameter of the tank). The ring can then be clamped at the top of the tank to prevent rotation.

For strength calculations, with sufficient rigidity, for both the baffles and the attachments, assume that 100% of the mixer torque will result in an equivalent force load on each baffle. Designing for four times the actual load will provide sufficient rigidity for the fluctuating mixer loads.