Sounds like you are enjoying cycling when on your RV vacations and doing some serious mileage.
If you want to haul anything of any weight from the grocery store or when you use your bike for daily excursions and need to carry lunch, clothing, gifts etc, can I suggest a one or if you want it balanced, a two pannier system that would sit over your back axel and minimize interference with the front steering. They can be removed and mounted easily.
They fit nicely on any rear rack and can be of any size. Some come with shoulder straps so you can use them while shopping. If on a budget, it might be an idea to search Craig's List or second hand stores.
The panniers in the photo are for long distance touring but they make a variety of sizes and quality depending on your needs.
Grossglockner, Austria, Aug/2013