Just as an option for you, I have purchased Model A body to frame welting from "Mac's" Model A parts to use for this purpose.
Any of the Model A suppliers out there have this stuff.
They have a few different products available both flat and with a "beaded" edge. Some have glue applied so its just a matter of peal and stick. I have used this as a gasket between the bed and the frame when I assembled it to try to keep the squeaks down. My plan is to insert it between the fender vent tubes where they connect to the firewall and also between the grill and fenders. It gives a more finished look to the under hood area.