I have a home made one I designed/built for my tube-VT52 class AB, triamp/solid state bass, high end stereo... it sequences 3 layers on and back down (missed on the Carvin was the power down side)... I also used magnetic relays (this was in 1976, there were no solid state relays then)... used RC timers (no microprocessors/microcontrollers in 1975/6).... analog baby...
Mine is 2U (just due to that was the size of rear boxes I could get)...
The carvin looks good but needs the down sequence...