I'm with you on this one Sundogz.
Double the amperage on the ESC for your calculated/estimated/rated load.
Also use an ESC that is rated for a higher voltage than the voltage being used. So if for example you are using 4s. select an ESC that will take 6s, with the cut outs set for 4s of course.
That way any amp spikes & voltage spikes will be absorbed by the ESC without blowing it, unless it's a dead short in the system that is.
Batteries are another thing. I like to make sure the batteries can deliver at least 50% more amps than the current draw of the setup. This also makes life easier for the ESC.
Also, with the full throttle thing, these are basically the same ESCs as used in helicopters & planes where they run at part throttle for a lot of the time.
Although too much part throttle does build up the heat, a suitably sized & cooled ESC should work OK especially in a lower amp draw situation like a tug breid.
Here's a couple of reversing ESCs for you to look at.

[link]http://www.himodel.com/electric/HiModel_FLY_Seires_40A_Brushless_Speed_Control_for _boats_W_Reverse_function_Type_NAVY_FLY-40-OPTO.html[/link]

[link]http://www.himodel.com/electric/HiModel_FLY_Seires_70A_Brushless_Speed_Control_for _boats_W_Reverse_function_Type_NAVY_FLY-70-OPTO.html[/link]

Cheers.
Paul.