Now I'm confused, Les. You have been plugged into a 20 amp circuit, have checked your adapters, but can't find where to buy a 50 to 30 amp adapter? How are you getting your 50 amp cord down to a 15/20 amp outlet without a 50/30 adapter? Or are you saying you are suspicious of the one you already have (even though you've checked it) and want to try a new one? As Richard said, there are ready sources for them, including small box and big box hardware stores everywhere. Admittedly, I have been in a couple hardware stores over the years that didn't have one in stock.
One problem could be voltage drop over too long of a cord arrangement, esp. if the first cord out of the outlet is a standard orange one designed for 15 amps. That's part of what screwed my 15/20 to 30 amp adapter a few years ago, while the coach was stored, and caused some wierd cycling of the rig's transfer switch. I splurged on a heavier duty outdoor 3 wire 12 guage cord (yellow), and stopped using orange 14-16 guage cords, even though storage never draws much current. If you want to stick with the 20 amp outlet, try a 15 or 25 ft. 12 guage cord, in case voltage drop is causing the transfer switch to trip that circuit's GFCI.
I don't see why you don't just plug the coach cord into the 50 amp outlet you say the electricians wired a 30 amp circuit to in your shop. It won't have 2 120v. legs like a 50, but should safely supply 30 amps. They may have used a 50 amp outlet so you could plug a 50 amp RV cord directly in without adapting. If the cord isn't long enough, I'd switch the outlet to the 30 amp the breaker and wire were designed for, and use 25 ft. of 30 amp cord and keep a 30-50 adapter on its female end; if you aren't already, you should be carrying that arrangement with you in the coach anyway - it can be useful in some camping situations.
Keith, not all campers use 30 or 50 amp systems. If tenters are in the site, alone or accompanying a big rig, they can use a 15/20 outlet. And so can park personnel when doing site maintenance with power tools and such. Because of the outdoor potentially wet locations, code requires the 15/20s be exclusively Ground Fault Circuit Interupter outlets. As Ed said, the 30/50 outlets are not "terminal" circuits, just feeders that supply smaller circuits downstream in the coach; those coach circuits are "terminal" or end-use/point-of-use circuits, and already have GFCIs protecting them (or should have).
Joel
