Unfortunately I have spent many hours working on VW's on a gravel
surface..  The job that you have to do won't actually be that bad
though,, at least you aren't pulling the tranny or replacing the cv
joints or something that keeps you on your back...

The only things that I have found is that:

you do want to use a plate of some kind to keep the jack from sinking

you need to be extremely careful with any small parts because you
could be stuck looking through gravel for hours for a dropped part.
(really)

Home Depot and Lowes type places have nice foam mats that you can lay
on,, the one that I use consists lightweight but stiff foam squares
that piece together like jigsaw puzzle pieces.  You can build a pad
for that is comfortable and that will help you find dropped parts.. 
This stuff is really cheap so you don't have to worry about getting it
oil soaked etc..

Jonathan Poole