I used the 3M brand rubberized coating, but only because my local parts place had them on sale. The generic brands are probably just as effective. With 4 cans purchased I used one can per wheel and could probably have gotten away with two per wheel!

Anyway, with the wheel off I put one trash bag over the axle and another over the coilovers in the front and spring/shock in the rear. Using very wide painters tape I then taped over any exposed sway bars or control arms, as well as the painted edge of the fenders than wrap up into the wheel well.

The oem rubberized coating in the wheel wells on my truck was very sparse and just had a small strip at the top of the well. Overall it was certainly a noticable improvement. The sound of the more aggressive tires is almost back to stock levels..(confirmed by my highly calibrated wife-to-be). An unexpected benefit was that when driving in the rain, it was much more quiet! Before, even with stock tires, I could hear the rain spraying off the rear wheels in the wheel well. This is now almost totally gone.

I would love to take it to the next level and hit the full underbody, it seems that would certainly work great. However, I would probably have to enlist a professional to take care of this for me if it wasn't too expensive.

Hope that helps!