The eternal debate of spring undercoating vs fall undercoating.

IMHO, you only really need to get your car undercoated once every 3-5 years, as undecoating is not meant to be washed off/cleaned, and it doesn't really matter when you get it done as they clean the underside of your car anyway before applying it. What you do want to get every year done is your car rust proofed, where they spray rust proof liquid into the nooks and crannies of your car to push moisture out, and it's debatable when you want to get it done, but usually people do this in the fall because otherwise the weather warms up and that thins the coating a lot.