Hi there guys,
Just came back from 3 weeks in Mexico with my wife (not in our RT) after spending some 60 days in South Carolina. I went through my SC travel expenses and if I consider my basic expenses, (gas, camping fees, food, propane), it came down to an average of 45$ US/day. I love to cook my own food and have 1 cocktail and 1-2 glasses of wine with my dinner. Never ate at a restaurant, nor went on a tour or amusement activity. So this cost is very conservative. Coming down from Quebec City and getting back totaled a little over 2400 miles and must be considered as one of my major expenses. I stayed in State Parks which costs between 25-29$/day (water, electricity).
300$/month gives you some 10$/day which I believe to be under the average per diem cost of staying home and only spending on food and gas (getting a video, grocery, etc.).
You should not only provide for unexpected expenses (RV repairs, non covered health expenses) but also for unplanned expenses you would carry under a normal lifestyle (gifts, useful stuff for your RV and for your home) given the opportunities a travels often brings you). As an example, it cost me some 900$ to repair my Onan and get a new battery. Even if I had a Skype Internet phone (15$/year, I had to move around in my RT to find a WiFi access point and spent some 150$ on long distance phone calls (made and received) on my cell.