[ed s]

Greetings,
Looking for some ideas from you guys.
My rig has three a/c units and the one in the garage I need to run all the time when we are at dog shows this time of year. Most dog show sites do not have 50 amp so here is what I want to do. I want to splice into the power line to the garage a/c, run the power line to some sort of wall mounted switch box and feed the a/c from either the coach or directly from shore power thru a plug end installed outside the coach.
A box with a switch that I flip the switch one way and the a/s us powered by the coach, flip the switch the other way and it is powered by the exterior plug to shore power.

Any one have any ideas what kind of switch box I can use and where I may find one.

Thanks

Ed