i am a PPG certified autobody tech / painter.
ALL car manufacturers dip their cars in a vat of epoxy prime these days. this is referred to as Ecoat. they paint the exposed panels with color and over spray gets in some areas on the bottom of the car. the areas not covered get left as is and driven. some arears get rusproofing sprayed in some areas to further protect them.
this is how the old mopars were painted back in the day.

all major paint manufacturers make tintable sealers. you could look into that.
they also make tintable bedliner.
https://www.amazon.com/Raptor-Tintable-Urethane-Spray-Liters/dp/B01CKE7M7M/

SEM makes spray bombs that are close matchers to factory Ecoat primers. i use this all of the time when working on inner panels of cars for corrosion protection.
https://www.semproducts.com/product/ez-coattm

in my OPINION. if you are looking for maximum durability. i would get a sample of the Ecoat you want to match. take it to a paint store and get a eye match mix of urethane single stage enamel paint made.
$$$ but it's durable. you could cut costs and use regular enamel paint. a LOT of people just spray the exterior color on the bottom and leave it that way.

there are large amount of under hood color mixes listed in paint code year color catalogs also. you could check these color for a match also.

i myself make a mix of epoxy primer that's close to original color and spray away and call it a day. the old cars rusted vbecause they were driven almosy every day and usually not taken care of. a restored car won't have this problem.