Tapping power off the DC jack of Uno

Why not put a panel mount jack on the sidewall and break off the DC to your 2 locations from there?
Ok, I reread - you want the connectors to be accessible so you plug in direcytly.
I would go with soldering to the bottom of the board at the jack itself then, the metal the jack pin will keep all that current from having to go thru the board traces as well.