wrenchin,i'm sure there are caulks/sealants suitable,but I'm with Alvin on this one.
Sealants can be messy.JMO

Is your choice not to use welting a cosmetic one?

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.