Painting inside of frame rails

That is the exactly an old sandblast gun i have . ill try this out thanks a lot

Yep, those work to.:D
I put a pair of hemostats on the supply hose so I can shut the flow off.
Might be a good idea with a sandblast gun because it might have a lot more volume than a regular air gun.

Though kind of comical to picture, I would hate to find out you ended up rolling around on the ground in a big puddle of POR trying to stop the flow.