Lantley wrote:
An RVsafepower transfer switch will allow you to tap into the 20 amp outlet on a 30 amp site. It will also work on GFCI circuits.
I own one and it works great.
I have use it at several state parks. It allows me to run both A/C's on a 30 amp site without issue.
RV Safepower (modern cheater box)
And I thought 100 for the PSRV product was steep
But yes. This is the best way to do it. 100% protected and will work.
It is what I would recommend less you can get the PSRV product which far as I know is no longer made or have the skills to make one yourself.