Well, tape the ever loving shiznit out of your running boards, because XP chassis take on water faster then the Titanic. Heck, the Rev chassis aren't much better. And no, you don't have to take off the snow flap, but if your running a 1.75 inch track (snowcross?), you might want to swap to a 1 incher, because to tall of a lug can build water underneath the tunnel and actually slow your track down enough to sink the sled.
The best advice is to go buy a ZX chassis 600 or better sled and that thing might as well be a boat, cause she'll run water all day and into the night.
Complete agreement on the ZX Chassis. 2000-2002 800 goes forever. For that matter, a Formula III 600/700 triple is even better. Rev/XPs are fine for puddle jumping but a guaranteed sink for entire lake crossings.