Edward,
I don't know anything about that rig - but don't install drum brakes on any small to medium boat trailer (i.e. - any bass boat and smaller). If they came with drum brakes, I'd replace them with disk brakes anyway instead of dealing with the headaches associated with maintaining marine drum brakes.
You aren't going to get away that cheap with either drum or disk brakes either, as you are going to have to buy a hydraulic actuator to get the fluid to either one. Tie Down makes the actuators of the ones I've installed. I've also installed both Tie Down and Kodiak brake systems, and I greatly prefer Kodiak for an aftermarket system between the two. Here's a link for shopping convenience to find prices, etc...
http://www.trailerpartsdepot.com/landingpage.asp?pg=trailerbrakes.htm&gclid=CMqc99zTnJsCFRyfnAodlmwEtg
You're going to need two hubs / caliper / rotor setups - like these:
http://www.trailerpartsdepot.com/items.asp?Cc=DISC-BRA&iTpStatus=0&Tp=&Bc= (The Kodiaks are better quality in this regard)
Also: tubing kit, hydraulic actuator, and a reverse solenoid
All the best,
Glenn