Treatment for wood enclosures

[Wrath]

I know i'm going to regret asking this stupid question, but sometimes its hard to get things through my thick skull:

For homemade wooden enclosures, do you guys coat the inside with anything? Some sort of finish, or shelfpaper or something to preserve the wood?

Danke

[Paleosuchus]

I use polyurethane with stain added for more color. Water proofs it and protects it.
Jason

[emkovar]

I used marine enamel to finish the inside of my wooden enclosure. And I siliconed all the joints.