Thoughts on bedliner for undercoating a car...are there any downsides?

[cpd004]

I've read quite a few opinions on applying a truck bed coating to the underside of an older car. Some say it will crack and others say water will get behind it and cause rust. For those that have done it and drive there cars even in rain, have you had any issues? Are any products better than others (Herculiner, UPOL, Rustoleum, etc)? I understand prep is most important.

[dhutton]

I haven't driven in the rain but I use SEM bedliner over 2 coats of SPI epoxy applied within the recoat window for good adhesion. I doubt water will get behind it and rust. I remove all factory undercoating and thoroughly degrease and media blast before applying the epoxy. The SEM bedliner has a shiny finish which is easy to keep clean.

Don