Lane-
Here's the link to the discussion of my electric set up:
http://www.c-brats.com/viewtopic.php?t=1263
It works great trolling for trout up to 2 mph in fresh water lakes. It has 44 lbs of thrust, and with 4 group 27 batteries, will run for about 9 hours w/o serious recharging.
They also make double and triple motor jobs with up to 165 lbs, but the battery drain on these bigger units is awsome. Mine draws 36 amps at full power and the 165 would draw 140 amps!!! I actually troll at about 60-70% of full throttle, or about 20-25 amps of draw.
What I think Tom (starcraft) means about getting a gas motor for salt water use is that you generally need a stronger motor in saltwater trolling. Saltwater models are made, but might not have the power to deal with the heavier wind, current, chop, etc. and/or the battery drain would be prohibitive.
Both MinKota and MotorGuide make engine mounted models, and there are a couple of smaller outfits that convert regular transom mount models over to engine mounted models as well. Let me know if you have further questions after reading the discussion linked above! Joe.