Yeah, don't use silicone. There are plenty of seam sealers available that will last longer. Lots of silicone sealant is also corrosive. The ones that smell like vinegar when you open them. I think it's acetic acid.
I used a self leveling seam sealer from SEM when I did the drip rail on my '65 and and a 3M sealer for other areas of cab. Both worked well.


Tradin' up dimes for nickels...
'`'`'`'`'`'`
My \'65 Chevy C-20