I wish there was a standard...but there isn't.
For my system, I cut a "clearance" hole in the sub panel and reinforced it with aluminum angle, as specified by Vans. In this hole I built a rack that will hold the Dual EFII ECUs, GTR20 com, GAD29, and GEA24, and PLX F/R Amp.
I am in the process of wiring the GEA24 now...there are LOTS of wires...
Aerospace Engineer '88
Structure - 90% Done
Cabin Top - Aaarrghhh...
Doors - Done
290 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Dues Paid 2018,...Thanks DR+