X3, only I'd say to stop at a thrift store on your travels and pick up 50' for a buck or two.
When mine started acting up, I too thought it was the coax between the wet compartment where the incoming cable is attached and the electronics cabinet at the front of the RV.
No, it was the switching unit that was bad. A direct connection from the end of the cable in that cabinet to the TV was all it took to clear up the signal. No more than 3 feet long and a male to male coupler. Cost all of $1.25. Now I need to fix or replace that switch box.