Surge brakes may be applied on a downgrade. If you are on level ground and they are adjusted properly, they will not overheat.
For the time being, put in a master cylinder and probably wheel cylinders on all 4 wheels. If your backing plates are still good, just replace the parts as needed.
Be aware that electric brakes will more than likly require you to have 4 new drums so that may be an expense you haven't realized yet.
Well...I am asking the same question about electric brakes.
I know "regular" electric brakes cannot (should not) be submerged in salt water or any water for that matter.
But I have not been able to find anyone who has tried Fulton Performance electric boat trailer brakes that are actually DESIGNED to be submerged in salt water.
Anyone know about them?