Ok after trial and error, I managed to 3 medal the 3rd stage.

What I did was place a relatively weak team at 26k power at the top camp along with a very fast Helper at about 600 speed. That way my weak team would reach the boss and die there. The Helper Squad was fast enough to clear the remaining two enemies at the top route.

At the bottom node I put a little slow squad at 484 speed to quickly go through the hurricanes. The other two squads (at about 540 speed both) went in the middle camp.