You seemed to be interested in doing the job yourself I thought. If so you can do this in one day and it is all bolt on stuff. If you don't feel comfortable bleeding the brakes once on then just have someone do that... I was told by the folks at my local trailer shop (who wanted me to spring for a $1000 surge brake job)...
The only thing you need to have on the axles is the mounting barcket....

...that is on the bottom axle above that I made. The top axle is the stock Mac axle that was on my trailer and has no bracket on it for brakes of any type. If you axle/axles has that bracket on the axle the job is all bolt on, just read how to adjust the tension on the spindle nut, but you will have to do that any time you would re-pact the wheel bearings anyway.
The surge kit above does have the break-away that applies them, so they are legal.
If I lived there I'd be glad to help you, the job isn't bad and if you got the kit I posted I'll bet you could find someone who on an off day from work would do the work for under $100.
Also you can't compare the water that the brakes see in normal highway use vs. going into the water, especially salt water. My truck that I posted a picture of has 150,000 miles with no brake problems until I ran through that salt water a couple times going on and off the salt. Granted it had a higher concentration of salt than even salt water, but you will still get the same effect. Why put on brakes with more moving parts to rust up if you don't have to. If you already have them and want to mantain them then that can be a different story,
Good luck with whatever road you take and any type brake if they are working are better than no brakes or brakes that aren't working,
Sum
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