I used the standard motor/propshaft/prop in my converted Seaport and it works really well. I run it with 6Volt Lead Acid Battery, Mktronics 10 amp ESC, and Planet RX. Servo is one of the standard Hi-Tech. Great combination , runs for a very long time at good speed and the motor doesn't get hot or even warm. Some have said they found the setup noisy, but with good lubrication I find it OK.
I have three or four of the Graupner 400 units, both in Speed and Eco form, none of them run hot. I'm just installing one in a small Slipway Trent Lifeboat kit, but this will have a 7.2 Volt battery to give a little more "go".....No water cooling is installed. I always secure my motors with a good two part epoxy, having learnt my lesson when one of the Graupner 600,s "came loose" in my Dark Class MTB.
Regards
Alan