under coating

[tobins 52 gmc]

What would be a good paintable undercoating

[BigJock]

If paintable,you mean 'brushable' I find it hard to see past POR-15.
I've used it extensively on my '50.

If you stick to the manufacturers instructions it works well.
There's the UV sensitivity issue,but you can overcoat it.
It flows out to a real nice gloss,covers well and is as hard as nails.

I painted the underside of my cab and fenders etc, as I figured if the sun gets to them i've got bigger problems to worry about.
I fully intend to keep my truck right side up!

I'm not a huge fan of the textured undercoats,my logic being the rough finish provides a 'key' for the crud and crap to stick too,whereas a glossy finish can be blasted clean with a power washer.

IMO it looks better too.
Just my 0.02c