Has anyone ever used any sprays or paints to protect the cabinet of a speaker?

Erik, thanks.  I'll look into some clear poly. 

deeznutz, yes I am aware of that.  My intention isn't to try "convert" these speakers into outdoor speakers.  I simply want to minimize any damage that  the elements will inevitably cause.  I only take them out maybe twice a week, and never in the sun.   If they were a lot more expensive speakers, believe me, I would never take them out...maybe.  :)

Loomis, that's really amazing.  I don't expect mine to last more than 5 years if I did what you did.  The summer sun we get is brutal for about 4 hours where i usually have them.  But good to know.  

Erik, per your suggestion, I found just the ticket.  Rustoleum has a clear urethane with UV.  I thought you were joking about the UV.  So yeah, I sprayed them puppies over the weekend.  They look much darker now, and cooler!  Thanks, man!