Usually harrassment of some sort will work. OK snake lovers don't freak out, I didn't say kill them. Agree, clear out any food items. Clear out leaves and debris as it will harbor bugs and worms [aka snake food], I sprayed a rat snake hanging out of a hole in my room [house] soffit with bug spray. Never saw him again. I hate mice so the snakes are a catch 22. Snakes kill mice [which is ok] but they can also get in any hole that will let a mouse inside your RV. Another reason to plug all holes around cables, gas lines, etc.
Finally I move from the city after 55 years of urban life. Now live in a very rural area on an old tobacco farm. Snakes are normal around here. The rat snakes I mentioned above are good to have around [just not hanging from my soffit on the front porch] so I have learned to just move them outt of my way if I'm mowing or what ever. The garter snakes you have are also harmless and typically very small. If you can catch them just take them a couple hundred yards to the edge of the campgrounds and I don't think if will return.
Good luck, I don't like to be surprised either.