Quote:
Dirtnut :
i thought about using expanding spray foam in the tubes. drill a small hole in the middle to fit the straw nozzel in and a small hole at either end to let the air escape as the foam is injected,this should help insulate & keep the steel from sweating.
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I strongly advise you not to do this.
These foams make a so called 'skin' on the contact surface. As they do not glue to metal too well, air and water will get trapped between the foam and metal and accelerate corrosion. These foams are even able to absorb water in their outer layers where the gasbubbles are open.
My tatra which was converted to a mobile hunting home by the previous owner was isolated with this spray foam and when restoring it i found that the wooden frame and metal were rotten. This was after a 3 year period. When removing the foam i had to use cloths to take up the water trapped between. It was hard to believe that so much water could be there. The oak frame was in places a sponge, I am not kidding you, you could take out pieces of wood and press out the water by hand.
just to give a bit of an argument to my advise.