Hi Dogfish!
I just ran my 7'Waterskeeter with a 38# electric around a small lake near Concrete. First I set it up on stands & hung the motor & battery to check the center of gravity. It was motor heavy so I made some adjustments. I would advise you to test in still water before you hit the river. I have to move the center of gravity forward with a modification to the seat position. Then I'll go back to the puddle & retest before I put it in the Skagit.
It will have it's limitations, but I think you'll find it to be a very versital craft with the addition of the motor.
Good Luck, Jeff