I have completed the installation of metal GT flares front and rear, these were butt welded. And I have installed the GT rear stiffening kit. All welds were ground smooth and seam sealer was applied where needed. I then applied a oil based rust preventative primer and then 2 brushed coats of a oil based high gloss enamel paint. I was going to apply one more coat via spray as a finish coat but before I do that I'm wondering if I should spray undercoating in the wheelwells? I live in Florida so not many rocks to kick up and no road salt. So should I just apply a finish coat of paint or undercoat? If I undercoat is there any advantage to applying paint over the undercoat? I kinda like the look of the painted inner fenders.

Porsche, Mercedes, BMW factory recommended replacement material

Comes in bulk and spray cans. Black, gray and tan.
Goes on thin, can be left as is or painted over. It's the stuff!
You still need to prime and apply a base to the metal under the wells.
The product is urethane based. Not greasy like body shutz.

For what it's worth my 75 chassis appears to have come from the factory with the inner fender wells just painted. I see no evidence of any undercoat,stone guard or similiar product.

It sounds like you have plenty of rust protection. However, if you are doing a nice paint job, I would coat the inside of the fender wells with a protective coating to prevent rocks and stones from being thrown up and dinging the body work and paint. If a pebble gets tossed up it will leave a nice star in the paint. The GT flares are really flat on top and would be most susceptible.

I used a truck bed liner material on mine. The flat areas are quite thick and taper to thinner as the body gets more vertical.

It's good insurance considering the cost of painting. YMMV

Did you use the spray can of bedliner or the roll on kit? And did you top coat over that with paint?

gallon can and a shutz gun

That was pretty funny.....

"I live in Florida ....and no road salt"

Wonder why cars (particularly Hondas) rust like crazy down there?

It's the salt spray that envelops your car when you get near the beach as well as the constant rain....

Never saw a Florida car last that wasn't undercoated to the max.

Down there they call it "Florida cancer"...

It's yer choice to sunscreen your body and yer choice to undercoat the car.

Ken