To protect inside the chassis rails, get a few cans of fish oil or lanolin, and a length of stiff small diameter sprinkler tubing. block one end of tubing and poke lots of small holes in the blocked end of tubing (length ways) for 5cm or so, poke down chassis rail, attach open end to can and squirt as you slowly pull the hose back out. I used 2 cans per rail. bit stinky for a while though.

