Hi @ChronicMcBudz,
Some bad experience with wet particle board had me swear off wood for cabinets.
Wood harbors fungi and in my case that was bud rot.
The time you spend waterproofing the interior will be paid back hopefully by problem free grows.
I would seriously consider using at least a boat paint for the interior.
Caulk all joints with 50 yr caulk too.
I was impatient and anxious to start my growing and failed to do the above.
I spent so much time hanging the door if I were ever to build another or adapt a bought cab I would make the door removable with full length latches to hold it secure.
That way it is really able to be light proof.
But if you keep the hinges, look around for articles that use bicycle inner tubes for light blocks.