protection steel on the inside of an enclosed space

[bigbear69]

Hi,
I am attaching a scoop with boarding platform /steps etc to a steel hull yacht.the boarding platform will be inbuilt how do I protect the steel on the inside of this once is all welded up.
also planning on adding a overhead structure on the stern put solar panels and to hang the davits off. thinking of fabricating from steel and they will be hollow so need to protect the steel on the inside also.
i've heard of filling the enclosed space with diesel,The yacht has a diesel filled keel, is this the only way to protect the steel. or can I coat the inside before i install ?
Any help would be much appreciated.
cheers

[CDK]

Hollow structures on large ships are spray-coated with Tectyl, Waxoil or similar wax-like products by people in protective clothing and external air supply, who descend through manholes. Smaller structures are treated the same way by drilling holes in strategic places and using thin tubes with a 360 degrees nozzle head. The holes are closed afterwards with rubber plugs.
The companies that sell the chemicals also supply the equipment to apply it.