This is a vat we made several years ago when we started using moulds larger than 8½×11 inches. A local farmer sells used drums and barrels as a side business, so we purchased a 200L polyethylene drum with an integral lid. We chose one that had been used for a food product (soy sauce, in this case) so we would not have to decontaminate it. A few minutes of work with a circular saw and we had it cut lengthwise, a little bit beyond center from the large bung hole. We used a sharp knife to deburr the cut edges, and added an elbow and ball valve to the bung hole to allow draining.
I made the two sides of the stand with ¼″ plywood and 2×2 spruce lumber. The cross braces are lighter lumber attached to the sides with ¼-20 screws with small handwheels for heads, going into tapped holes in the legs. This would allow for easy disassembly and storage.
The vat holds about 120L of pulp, but if it is not full, it can be rotated in its cradle so the water level is near the height of the lip. In this way the side of the vat does not form a wall that the mould must constantly be lifted over.
Because of its shape, it requires less water to fill and less fibre to charge than a rectangular vat of comparable dimensions, yet it is still easy to dip and raise the mould without hitting the sides or bottom. Sloshing of the water is, if anything, reduced compared to a rectangular vat as well.
Although we used hand-removable bolts to assemble the stand, we have never taken it apart. It turns out that when the vat is empty, the drum part can stand on its end within the legs, so there is little advantage in storage space to take the stand apart.