Duane: I realize your inquiry was specifically to Chuck, but the topic of trailer brakes is one of interest to many and there are many people who have some experience to offer. In that vein, I will provide a few comments and also recommend some other resources to you.
Disk brakes seem to be
de rigueur on trailers that will be immersed in saltwater.
Surge controllers for trailer brakes do seem to be a bit
passé these days, too.
I gave some consideration to overhauling my trailer brake system several years ago when one drum brake failed. Since my boat trailer only sees saltwater about once every five years (or longer), I decided that drum brakes would suffice. The cost was also a factor. (And, as things tend to happen, we have not had the trailer in saltwater since I replaced the drum brakes.)
The cost of conversion to disk brakes and an electric brake controller was quite significantly more than just re-fitting the drum brakes. I was able to replace all the drum brakes for about $440 and kept the surge controller, while a entirely new disk brake system with electric controller would have been at least $1,200. Even if I had gone to disk brakes with a surge controller, I would have needed a new surge controller due to the increased hydraulic pressure that must be applied with disk brakes.
If I were a coastal boater and launched from the trailer into saltwater all the time, I think conversion to disk brakes would make sense. The brakes seem to be better able to be flushed with fresh water and tend to have a longer service life compared to drum brakes.
As for going to an electrically operated brake controller from a surge controller, I suspect this decision depends more on what sort of highway travel and terrain will be encountered. Surge controllers are quite simple and generally reliable devices, and they do an acceptable job of providing braking. Electrical controller may not make a big improvement, except in certain situations. It would be nice to be able to apply only the trailer brakes in some situations, like when descending a long steep grade or if the trailer begins to fish-tail. I can still recall the panic I felt on one trip. We were descending a long downhill grade when a big crosswind hit. The trailer began to sway. Of course, I over-corrected, inducing a sway to the other direction, and thus the trailer started fish-tailing. The following ten seconds were very tense. I don't know if I would have had the presence of mind to reach down and manually apply electric trailer brakes, but in retrospect having that option would have been nice.
As for disk brakes, I see that KODIAK-brand seems to be a popular choice in saltwater boating regions. I am somewhat amazed at how many tiers of product they have in their line of brakes. If you choose the best-grade components--that is, the ones said to have the most resilience to saltwater--you can really spend a lot of money on Kodiak-brand disk brakes.
Here is a
link to a good discussion on trailer brakes. In the thread the links to photos are still working.
Here is a
link to the somewhat-hard-to-find website of Kodiak.
Here is a
link to an excellent series of photographs demonstrating installation of disk brakes in detail. The brakes used in this example are the Tie-Down Engineering brakes: