Any value in spraying undercoating before installing rear wheel liners? Will it help at all with dampening road noise or the like?

Any downsides other than the small added cost of a couple of spray cans and the time?

 

I have used undercaoting before, and the nice thing is with a new truck, it will be the best time to spray it in. If you spray it over rust, it will cause more rust. If you spray it over nice clean fresh paint (or in an aluminum body truck ) it should help keep the fender wells looking "black" but it you are putting liners in, I would probably spray rustoleum black spray paint, then the fender liners. Or use truck bedliner than the liners.