Treating the interior of a loudspeaker

I am debating if it is better to varnish or paint the inside surfaces of a speaker or leave them plain, I think there are pros and cons for doing it. Solvents could degrade glues used in the drivers but on the plus side materials like MDF would be more resistant against humidity.
I'm not sure I would worry about it too much. If you are concerned with "outgassing" then let the cabinet sit for a week after you coat it.

I will say that veneered cabinets generally come with the inside veneered in a lesser grade wood. I was always told that was to prevent any warpage from dissimilar surfaces and moisture absorption. If in doubt, finish the inside similar to how you finish the outside.

David S.