Never heard of Xylan coating have you? I bet it's the same as any other polymer coating that they charge HUGE $$$ for. You can do the same thing with a bottle of Rejex, NuFinish, Simoniz Ice or one of countless others, If they want to do the inside too that will include someone going in with a spray can or two of 3M Scotch Guard or similar product. Read the fine print, I bet if the stuff fails they will refund your money on a pro-rated basis, if they give you anything at all. Save your money this is one HUGE profit maker for the dealer. Hire some kid to wax your trailer if you think you need to. I wash mine a couple times a year. It still looks new.
B.O.