And given the size of the structure, how would it have to be applied?
Application would not be the problem, the chemistry of the compound being applied is the key.
I have used commercial and my own formulated, wood penetrating epoxies for rotten wood preservation. There other recent products. Mostly they are thin or thinned resins that penetrate. I have found they work in some circumstances but not others.
I have some historic iron objects (deck, wharf, and railroad rail, nails, spikes) that present their own problems depending where they resided. The worst are ones that have been in a salt environment and the major portion of the object is rust that is ready to flake off. I have some water based rust inhibiting chemicals but they exacerbate the flaking. I have resisted using any resins or oils because they obviously alter the appearance
An interesting case I am aware of was where a museum consulted a rust preventing chemical manufacturer (Cortec), on the preservation of a dinosaur fossil.
The fossil had a high iron content and was rusting once exposure to the air occurred. Cortec manufactures chemicals that emit corrosion inhibiting vapors used in industrial and military applications including electronics. They were able to provide an appropriate product.