I wouldn't recommend Galveston, but would Fluid Film. We've been on the lower coast (Rockport/Aransas Pass for 9 years. I tried various things on our first fifth wheel....it still rusted. We moved back on the water 11/2015, so I started looking at other products. I ran across a fellow on Mustang Island that sprays the Fluid Film. Several of us in ICW RV Park had our frames sprayed. Very pleased with the results. Plans are to spray every six months or so.
Fluid Film is available at our local Lowe's. I bought a can when I first found it through my research. I sprayed the rusty metal handle of a garden shovel my wife has. Days later, I scraped the rust off, and the film had penetrated the rust. I'm sold on it.
There are other issues to be addressed on the beach. I changed all the exterior screws on our previous fifth wheel to a high grade stainless, and have started doing so on our Rushmore. Another thing is the AC coils. The salt atmosphere will eat the aluminum fins on the condenser. I have looked at several coil protection sprays, but have not decided which one to try yet.
Hope this helps!