After reading your post, I streamed that movie just to see the bus (well, I also was an avid surfer for years
)...
After slowing it, pausing it, and replaying it...
that particular bus appeared to have moved the door and rear windows
forward about three window spaces, then opening the panels at rear.
In other words, the porch was just the back of the bus (original length) opened up, and then re-sealing it closer towards the front...
Pretty cool actually!