How would you make such a board?
For a start, I'd be thinking about putting them rececpts in some sort of an enclosure or two, more than likely a weather-proof one, with a top-hinged lid so that the sockets can still be used with the cover in place.
Secondly, there'd be some sort of point of attachment below the enclosures so that any flexes that were connected to the sockets could be supported, meaning that the sockets weren't carrying the wieght of the cord.
Thirdly, all the wiring from the disconnect to the enclosures, would be in conduit.
Just a question though,
Is there really a need for 60 (30 x 2) repectacles, all in one place?
This is just asking for a tripping hazard!