Don't seal the bottom of the tube with concrete.
There will be times when you get condensation inside the tube. You will end
up with a tube with a couple of feet of water in the bottom. Can you say
rustout in a short period of time?

OK, right now I plan to FILL the tubes with concrete, like a
Lally column. Sound OK???

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Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?