Just remember... When wet sanding!!!
Dont apply to much pressure- let the grit do the work, and the water will actually pull the paper to the substrate. You can do damage by using 400 grit and pushing hard. It'll come back out, but as I said- use your lighter grades first to test and get a feel for it- you can try 1200 on some- you'll be surprised at what it does. The lighter paper you can get away with- the better off you'll be, and the faster it'll get done.
I had a nightmare the other night that I turned all you guys loose with Wet"n" Dry and you all hated me because you scratched up your trailers- so I feel a little caution should be exercised if you have no experience- its really simple and easy though, just don't get ahead of yourself!