It's a complicated design to engineer for sure. I would try a cheap piece of melamine across the entire back for support. I used zinc coated 1 5/8" drywall screws and pre-drilled all holes.

1/2 a sheet would have got you a 5 high 28qt rack. I get 11 high out of one sheet. Here is two V-18 racks stacked, a 10 high 28qt rack and an 11 high 28qt rack.



11 high 41qt rack (two full sheets):



I would use all 4" heat tape and just get a HerpStat 1. More than enough to handle to load.