Best seam sealer

[T.W.Dustin]

My cab is hand stripped to bare metal and I am starting on bodywork. I don't have any rust issues. I stripped all of the factory seam sealer out of the rain gutter, stripped where the rockers spot weld on to the cab pillars, etc.... I can't remember the brand of sealer I used the last time I painted my '38 Dodge and I can't find it online.

I will etch prime ahead of sealing. I plan to paint with Summit Hot Rod Flat red Acrylic Urethane paint.

What is the best seam sealer to use here and also in the floor, etc...? I am painting myself. This truck will be a regular driver sitting outside a lot in the AZ sun year 'round.

Thanks, Tom