[Showdown]

Chiming in a bit late, and with a comment that would have been best at the outset… oh well

Having built a lot of bentwood furniture the best way to approach this is with a mule and laminating veneer. There’s really no other way to ensure an even and unwarped piece.

Yes, it’s more work but the results will be better and you’ll have the capacity to make more with less effort.

Another approach that’s not necessarily less labor intensive but doesn’t result in an extra mule is to fabricate the shape out of foam and then cover it with fiberglass, then body filler. This is super lightweight, can be made really smooth and allows complex compound shapes that laminating veneer has a hard time with.

Rigid foam insulation from home centers can be glued together to make the shape, it cuts and sands really well and it’s super cheap. The one catch is that you have to use epoxy resins as they won’t melt the foam.

The water-bent plywood approach will always want to return to a flatter state and I fear you’re going to continue to see distortion as it’s exposed to heat and humidity changes.