the battery and motor obviously add significant weight to the whole rig, battery is 53lbs alone and motor i'm guessing around 25. The wood for the mounts is really not significant compared to that. I am about 160lbs riding in the back and tested it out with my brother at about 200lbs up front. Lots of gear including paddles, life jackets, tackle bags, and a cooler with half a dozen bottles of water and snacks and it was riding just fine in the water. Not too low at all compared to without the new additions. Would i want to haul the new stuff around portaging; absolutely not, but i also wouldn't want to portage too much with my beast of a canoe anyways.
That being said i will be doing a 5 day trip up north in september and am undecided if i want to bring the motor for the first bit of it and stash it to pick up on the way back...