Re: stop trailer rust idea
a sealed 1' section of 2 x 5" steel tube (as commonly used on trailers) will displace .52 gallons the displaced water weight is just over 4#. the steel itself weighs in at 6#. since the weight of the displaced water does not offset the tube weight, the sealed 1' section of 2 x 5" steel tube will sink. does not matter if you add foam to it, helium, or fill it with 5 psi or 3000 psi of air. Now if you let the tube expand by 50%, so that the weight of the tube is still 6#, however it now displaces .8 gallons of water - it will float.
same reason dive tanks sink, however if you take the air within the dive tank and let it fill a balloon, you can raise a ship with it.
Take the same tube, now add the 0.07 cubic feet of foam at 2#/cubic feet. and you add 0.14# to the tube and you do not increase its floatation because you still have not increased its ability to displace water.
I know that the weight of my trailer still overcomes its displacement no mater what its filled with (water, air, rust, foam, oil, frogs, baby rats). Trailer still sinks
I think I would stick with grease or a fluid film.
