I've searched for this, I hope it hasn't been covered before! What would be wrong with using the breaker bracket/busbar assembly from a 125a sub panel inside my control box? I think it would make it very simple. Just feed the box with either a 50 or 60 amp cord to the busbar and use a 2 pole breaker for each 5500 watt element. Add a 15a breaker for the pump(s) and a fuse for the PID/SSR. It should be safe, and allow for future changes in design. I'll use a GFCI at the main panel.
It shouldn't be any more dangerous than your breaker box at home. Just kill the power before you go in. Once built, I won't be in there messing around.
I agree, your way is safer, but it's easy enough to pull the plug.
Yes, I'm sure that the DIN rail is better, nicer and maybe more cool. But I can't pick that stuff up at Lowe's. I thought the busbar arrangement of the breaker bracket would simplify things since I have no experience with DIN components. I was pretty sure that the terminal strips in the nice setups were exposed with raw power also.