I have to fit two 3mm bare steel 80mm by 80mm box posts into the ground. There is no room for a base plate and bolts to fix them to a lump of concrete so I am going to treat them like fence posts. As the first 400mm down in the hole is unstable due to decking etc I have dug a hole 1200mm deep to take the posts. I am going to use Postcrete
The posts will stand about 2400mm above the hole and have a horizontal force of about 60kg at about 2700mm above the solid ground.
What are the best options to avoid the post rusting when its in the ground.
Obviously painting the outside and covering the top.
Paint the inside?
Foam fill the inside?
Concrete the inside?
Cap the top and bottom?
Vent the top to let humidity out but no rain in?
Wrap the bottom in plastic but make sure no water can seep between the plastic and the metal?
Suggestions please.