Please post photo of said rat. Is this a New York size rat or a mouse size rat 2 legged or 4 legged?
Option: sit inside quietly with loaded shotgun, per VP Joe Biden, and fire above his/her little (or big) head when it pops up......kind of like "whack a mole"!
Option 2: trade the rv in immediately.
Option 3: find that entry point inside the living area and plug it with expanded foam from Home Depot. Minimize outside openings to a small enough opening they will choose to go to another rv versus yours.
If all of the above fail; and you do not wish to trade, get a BIG CAT and trust me, no more intrusive critters. Our cat is 16 lbs and HUGE. Her daddy weighs 26 lbs and is solid muscle. She is a Maine Coon, with claws and will end your concern! We rarely even have bugs. She can catch, trap and KILL the best!
ps: make sure you have the necessary hunting supplies on hand: couple of 6 packs and some cheese and crackers to pass the time away.