That sounds like it will work. If the Jr hooks up like a 104 then you can power it from the picoboo as well. The three trigger terminals on a picoboo, 12v+, 12v- and trigger. The output pir if just a single wire goes to the trigger input. Power the pir from the 12v+ and - terminals. If the pir output has 2 wires then one should go to 12v+ and the other to the trigger terminal. A picoboo triggers best with a normaly open setting on a pir, only becuase some picoboos will only trigger properly with a normaly open pir.
Do you fear whats waiting in the woods?