in response to the acid question, yes alumabrite, or pontoon cleaner, or any kind of acid based alum. cleaner, is just that, acid. You have to realize that this is not going to eat a hole in your tunnel, this is not a TV show. The stuff you can buy off the shelf is not that strong. What it does is de-oxidize the alum surface, bringing it back to the original state in which it was manufactured before air and salt had a chance to oxidize the surface. I have used this on trucks, sleds, trailers, and even airplanes. In fact it was a requirement to acid wash the bare alum. of the plane before we alodined it and painted it. If it was not acid washed (with a scotch brite pad too), the surface oxidation would keep the paint from properly adhering. Try it and you will be suprised how easy it is and how nice it looks. Just make sure it is rinsed off with water real good. If you let it dry on the surface it will turn it kind of chalky white, like the salt spray dried on the trailer after a trip north. No big deal, just re-apply the acid and rinse. Tip for summer storage... acid wash all the alum parts, rinse well, let dry and spray with WD-40, it will look great in the fall, no oxidation.
If you but the HCL/muratic acid in bulk (gallon) dilute with water about 3 p water to 1 p acid. And remember the saying..."do what ya oughta, add acid to wata"