For awhile I've wanted to switch the shore power from hard wired to a detachable cord. After some looking I decided the smart plug was the best way to go.
The next issue was going from a round hole with three bolts to a square plug. I bought a sheet of 1/4 inch marine starboard (hdpe) so basically a plastic sheet. Took out the current "mousehole" and used that as my starting template. Then i cut a square hole for the smart plug to fit through. Leaving a little air gap. Mounted the plug to the adaptor plate with some stainless bolts and was ready to cut the cord. Install on the trailer was relatively easy. Did a quick test pulled it off and put some silicone on the back and around it to seal it all up again. Very happy with how it all turned out.
I just installed a elect inlet adapter on the outside compartment door that goes under my sink. Then did the same on the inside. I then use an extension cord from the campground box so I can use a portable fire place inside the toy hauler. I do not trust the plug inside the rv because they are to small of a gauge wire.