Etching is usually a prelude to painting. Not sure why you'd want to etch, then take boat out in salt water for a test run. Take it out, then begin doing whatever you decide to do. Your boat is not going to dissolve during one test run.
Here in San Diego there are lots of boats used exclusively in salt water, 20 or more years old, similar to Gregor (my Bayrunner is like a second cousin). I can only recall seeing one that had the outside of the hull painted. Not saying it's a bad idea, but there's a lot of aluminum skiffs running around here w/o hull paint. Here's my hull (photo). Been that way since I bought it in '85. As I noted before, scour white spots off with a scotch brite pad and there's no pitting underneath.
I did have some corrosion, with pitting, where the hull meets the forward portions of the bunks, which I think is a result of sitting on soggy bunks/carpet during a 20 year dormant period. Nevertheless, this winter I'll be installing those glide sticks to minimize moisture being trapped in the future.
As far as I know, electrolysis won't occur if your boat is on a trailer on dry land. (and not filled with water). Don't see a need to disconnect battery for that reason.
You can raise the boat off the trailer to fiddle with the bunks, using the trailer as a jack and putting supports under the boat. Lots of posts on different sites on how to do this.