I have used Fluid Film on my Tundra for a number of years and it seems to work well.
One problem with undercoating applied after the fact that some are not aware of can be a BIG problem. At some point in time, undercoating WILL age and FAIL. When that happens water, road salt etc gets trapped between the undercoating and the metal surface it is supposed to protect. When that happens the metal starts rusting at a faster rate. The bonus problem is that with some undercoatings, you CANNOT see the rust happening as it is covered by the undercoating. That gives the rust a BIG headstart.
I have seen this happen on a number of vehicles including at least one I own. This is why I use Fluid Film each fall.
