Injecting Foam into Steel Structures - Good idea or not?

[Jeremy]

I'm currently doing a fair bit of fabrication work around my slide-out openings, and adding lots of steel box section for strength etc; this work has set me wondering again about whether there is any wisdom in injecting expanding foam inside the steel box section as a rust-preventative measure, and possibily even for insulation purposes etc. Will the foam prevent condensation forming and thus prevent rust, or possibly cause increased rust due to lack of ventilation / airflow inside the steel structure? Would I be better off injecting wax (eg Waxoyl etc), or just leaving the inside of the steel sections as uncoated steel and not worrying about it (which appears to be the approach the manufacturer took, with no ill-effects 22 years later as far as I can tell).

Jeremy

[tomhamrick]

Jeremy, When we stripped our Eagle we drilled 3/8" holes every 12" in all of our tubing and filled with spray foam. We sprayed until it came out the holes then it kept expanding out until it filled the cavity. When I am walking through a campground on a cool damp morning I can see the framing of most coaches, but ours never shows. That tells me the insulating value is worth the time as it stops heat and cold from passing through and into the coach. Also if condensation has no void to get in, I don't see how it can happen.
Tom Hamrick
1984 Eagle