A thwarte near the boat centre should be fine in my opinion but in all things structural, I defer to Matt.
What works for me is a lighter, permanent thwarte. In ADDITION to the permanent thwarte -
I make a removeable plank that fits across the gunwhales like this,
It is held down by a simple screw and clamping block like this,
that only takes moments to mount.
Other advantages for me are
1. The whole bracket is moveable to adjust so it has minimal impedement on my paddle stroke
2. I can loosen the two screws that hold it in place, and remove it with my sounder, rod holders and knife intact. This greatly reduces set up time at the waters edge.
My system is continually evolving as I "borrow"

other blokes ideas that I like. I really like YOUR ideas re a bow mount leccy on a canoe

Only problem I can see is how to get up the front to raise and lower it.
Do you know how to post piccies here mate?
