Ribbed flooring with a raised front sounds best so far. I don’t think a kiddie pool would work well or at least not long, and truck bed liner is a neat idea but my Snowbike is 10’ long and I’ve never seen one longer than 8’. Of course parking van on incline would be helpful except when leaving the snow park, it’s all downhill for quite a ways so that’s when I’m guessing stuff gets wet. If whatever it is has a lip on 3 sides and the back edge tucks down along the door edge then I can imagine it draining pretty well.
thanks!