Ok, here's my 2 bobs worth!
1. Go back to the dealer and see what he can/is willing to do about it. If it seems a lost cause, maybe suggest he contact Guang Sheng and at least mention to them next time about quality control in reference to the paint coatings etc.
2. Guang Sheng have their own website
http://www.gs-telescope.com/
Maybe even drop an email to them - sure they may not even respond, but then again they may.
If I were the manufacturer or even Dealer and knowing the power of the internet and these forums, I would do my best to come to the party in resolving the issue. Lets face it, if its costs approx $800 to buy, think how little the cost it would be to make, probably no more than $100.
If word gets around that they make decent optics, but average chassis/finishes some may start to think twice abt grabbing one.
Unfortunately as mentioned 99% of the dobs come from the same manufacturer - hmmm maybe that defeats my argument.
Failing all that as Mike said, either live with the rust or try removing it and then putting another coat of paint on it. Better still what about using some sticky contact paper with a nice floral pattern.
Sorry I shouldn't make light of an annoying problem, especially when you've parted with some good bucks.
It definitely sounds like the salt air has something to do with it and/or unfortunately you happen to just get a bad batch on the production line.
Good luck with the outcome. Will be interesting to know what happens.
Norm.