When snowbirding in Palm Springs, I subscribe to high-speed internet from Spectrum so I can stream my TV content via an Amazon Fire TV device and Hulu. It is provided via the normal cable TV connection at the site.
The first time I hooked up my router to a TV jack (the one with the amplifier), my internet speeds were very slow and intermittent. The Spectrum tech came out and identified the problem as "noise" being introduced by the amplifier circuitry. He said RV's are notorius for doing this.
The solution was to place the router in a "basement" compartment and connect it directly to the site's cable feed on the post. Works great.
I think that even if you are able to identify and fix the problem with your RV's wiring, the router may not work well when connected to it. Ultimatley, you may have to go with a solution similar to what I did.
Good Luck.