Advice needed on sealing the cabin to a Angle Iron Frame

[Windward Tom]

Hi All looking for some input.

I am at the point where I will be mounting the cabin structure to my frame. I have an Angle iron frame nice and reinforced. Had no choice to use this frame as it is what I had. My question is when I drop the body onto the frame for the final marriage, I want to seal the connection between the body and the angle iron frame as I feel water may work its way down into the angle and sit there. I have thought about 3m 5200, silicone, Flex paste, butyl tape, and various other sealers.
The body is sealed very well, plywood coated with CPES, enternabond wrapped around the bottom edge 3" up and along the bottom, all painted with fence post sealer. I still feel I should add a sealer of some sort into the inside edge of the angle to seal it and keep any water from getting in and rusting the frame from the inside.
Any ideas on what sealers will be best would be really appreciated. any past experience would be great. Again I know square tubing would have been best but I had the angle iron trailer so I had to use it.

Thank you so much in advance.

[Wrecit]

Personally I think it’s over kill but butal tape can be your friend (which is why I used it for the same thing on my enclosed trailer conversion lol)

Just put a good small bead of silicone over for your final seal