I'd say it depends on how much your boat weighs, and what kind of tires you want to run.
If your boat (and trailer) weigh 8,000lbs, your gonna need two 5K axles, and beefy tires to boot. Those low-profile car tires will not do well with a heavy load.
I have triples, and they do scrub in tight turns, but the tires expire before they wear out.
Get the best of both worlds- dually doubles!