Hi Sue H, I was advised to use something called Vulcam...it is a type of caulking.....bought it here in Tucson at the Airstream dealer--Oasis RV
Certainly someone who knows more than I will reply (hopefully) I envy you people having the project.
I recently "inspected" a 1959
Airstream here in Tucson for a forum member......made me wish I had a barn and room to take it apart and restore it.
Parts for older Airstreams are available....Inland Empire...can't remember the complete name....Andy gives advice here and owns a business that restores Airstreams....knows all about parts and availability of parts. I think Inland RV is in Corona, CA. Try googling it.