I'm assembling a 1966 Dodge Coronet Deluxe two door 6 cylinder 3 speed stick sedan that had some rust under the drivers feet and under the passenger side of the front seat. I've also put in a 4 speed hump so I"m asking on here what brand and type under coating will work out here in the northwest for a summer driver car, we're not on the wet side of the Cascades either
BTW, the car has never had undercoating so I'm going to replicate most of the cars I've seen out here on the west coast from the firewall pinch seam back under the floors to the rear wheel wells like a lot of the dealers did back then.
Thanks in advance for the help, Cab

Cab where you are undercoating is not really needed.

Unsure what to use as I never apply the mess in a can.

A couple thoughts:
Might be a dealership or accessory place near you that can do it with the "real" stuff, and they clean up the mess on the floor; last dealership I worked at had a bay dedicated to that at the bodyshop.
The rattle-can stuff seems a bit thin, so unless you've butt-welded the floor repairs, it won't usually have enough thickness.
Best stuff I've applied myself was Rest Rick's, kinda spendy for a non-OEM resto though.
Spray-on bedliner has a nicer consistency & finish; at the resto shop we use the Rhino Liner on Jeep & FJ40 pans and it's way nicer than undercoating, less messy to apply, dries hard and stone-proof; kit's about $100-$125 and comes in black or tintable. The big 2-part systems used at truck accessory places (done that too) use a heavier-weight material that would add at least 50 lbs to the car.

Use a quality brand rubberized undercoating, 3M body Schultz is very good and I think it comes in spray cans - or other aftermarket spray bomb. You want something that dries without remaining tacky.

I like the spray can bedliner available at any parts store. Goes on easy, is more durable than paint, much cleaner than undercoating and protects well

Having lived in Yakima for years I've found a great cost affective product that met my needs. Raptor, which can be found in many automotive paint supply places is inexpensive an d works really great in providing a barrier to protect the sheet metal on the bottom of your car.

I used it both inside and outside. It helps to have a lift to reach all the areas of your floors.

3M Body Schutz is the best beat and I think you can get it to look just like the factory stuff

Another vote for Raptor, we use it under trucks, Jeeps (underneath and in side the tubs)and under restomods. Great stuff, good looking finish when dry, cost effective, durable, easy to apply and even easy to patch should you damage it or scrap it off on something.

I used tinted yellow raptor on my interior and Lizard Skin Ceramic insulation on the underside of the car and roof. Isn't driving yet, so I can't comment on the improvement, but i expect substantial improvements.

TTT

I've tried the products from Napa. Their rocker guard gives a nice finish when applied with a schutz gun. Perfect thickness, uniform texture and dries nicely. Their undercoating on the other hand goes on thicker and doesn't dry very well.