Happy Mothers day.
I have the same set up as Bob, although this happened the 1st time I planned on using it.
I was at the marina I would be using a couple months prior to a planned trip and looked at the outlet which was 30 amp. So I made up the above rig and ready to go for four days at oregon coast in Feb. (blessed with a reasonable weather window). I come in at the end of the day with some bay dinner and glad to be with my visiting brother from Alaska, recuperating from hip surgery. I proceed to set up for the evening when I discover every pedestal on the dock arm I'm on is 20 amp. It turns out the dock arm I had checked earlier for sizing was for commercial/charter boats and the dock arms for recreational boats which I was assigned were 20 amp. Hmmm. We just ran the Wallas more without the quartz heater I had brought to suppliment, and had the right sleeping bags. We had good time. So I still have never used shore power at a dock, but am softening up some and will be in the future.
I guess an additional 20 amp rig of sorts for this type of marina is best.
Tom