Thanks guys. I think the consensus is that it's the overall length closed up including tongue. I'm going to make it 25' to give me some wiggle room. This is actually going to be a "temporary pad" so I'm not too worried about the next camper. I hope to be building a second garage in this area in the next couple of years and then I'll move the camper pad over behind the garage. It's not fun enough to do it once so I'd rather do it twice!
Kellys what kind of pad did you put down that you needed a permit (gravel or cement)? I'm putting down gravel and I kind of took for granted that I don't need to worry about a permit or anything... hopefully you were talking for cement.
Alright time to go get to work. Thanks for the replies.