I need to replace 2 rusting porch columns, and I'd like to replace
them with a couple of steel posts so I can have some options when it
comes time to make them look nice.

My porch is around 6' x 14', with a single support post at the two
ends not supported by the house.

Is there a particular type of steel pipe I should use for this? I'm
planning on encasing the pole in either masonry or wood, so I need it
to be fairly resistant to moisture, since it won't be visible. I'm in
North Florida, and the porch where these will be going is about 2 feet
off-grade, but water blows in during storms, though it does drain
nicely.

Thanks for any advice!
Nathan