Sealing inside of frame rails

[teranfirbt]

Hey all, did a little searching and couldn't find a specific answer for the easiest way to coat the insides of the frame rails to prevent rusting. I was looking at the Eastwood frame coating in a can, the stuff with a hose on the end, but it seems expensive for what it does. I also couldn't find much for accessing the insides of the tubes. Is there a go to product or method on the board for getting these guys coated? Would definitely give me some peace of mind up here in the damp northwest.

[Nissanman]

I used an aerosol can of Fish Oil. This stuff is deodorised and comes with a long applicator tube.
From memory I just sprayed it inside the chassis rails from the threaded holes already in the rails.
It mists up fairly well and if you spray for a length of time you can see it travels quite well and vents out other holes.
You could drill extra holes if you want and then plug them with a rubber blanking grommet.
The product I used is not suitable to paint over (it stays tacky) so it has to be the last step when restoring a chassis.
I have also used another product called Cavity Wax.
The container has a special screw on gun and a long nozzle so that you can use a compressor to apply the wax.