999th base 

Doing it through a hole in the roof of a moving caravan.

Guy: Duuuuuuuuude, do you wanna go to 999th base?

Girl: Have you got a caravan?

999th base by Jen der Bende September 25, 2007

99th base 

Webcam sex
two people both in a different area,put on their webcams, and the guy starts to pleasure themselves e.g masterbating and then the girl follows.

joe: i got to 99th base last night
sam: really?!
joe(has a smug look on his face): yeah man
sam: i really need a webcam :)

99th base by baseaddicts April 15, 2009