Wheel well undercoating
 

What is the best way to duplicate the factory undercoating in the wheel wells?

3M Body Schutz.

I shot these with a Shutz gun at 20 psi and 3M 08864.

I use a 3M product 08804 with their gun. Fairly inexpensive but takes a little practice with air pressure and overspray as it likes to go beyond where you are pointing so I used a piece of cardboard way out in front of the gun to limit this. In the end, it was worth the results.

That looks very good.

That looks really good. How far does a can go? Duplicating the factory application as shown in the assembly manual

If you are asking about my process, I typically used 3 cans per car. I would rather waste a can than run short mid spray so buy 4. I used fairly low air pressure and put it on in layers. If you try and put it on too thick it will run and sag and look terrible. Another tip, duct tape the plastic nozzle onto the car as the means of locking it on is not sure proof and when it come off, it will make a total mess as the can is under pressure. Ask me how I know.

What the factory did ? I used to undercoat new cars at Luby Chevrolet in Boston 1967- 1972 if the customer paid extra for undercoating.

My experience with either of the 2 3m products mentioned is adjusting the air pressure and distance can get the wide globules to somewhat replicate the original tar based undercoating but when you get the width, it's too flat. I use a shutz gun and UPOL bedliner in black. It can give you the body to build and widen the texture, and it comes in quart bottles, but I believe you have to buy a gallon which of course give you 4 bottles. It does cure much harder than the 3m. You could top the UPOL with 3m and get a bit closer to the OEM appearance.

That is true for full body undercoating. But, the factory undercoated the bottom side of inner fenders as well as the inside of quarter panels.

I think that is what the OP was referring to.