I have a P3 controller, love it. Nice display for all the information you may want, without needing to decipher any codes.
Do you, by chance, have heated front seats in your Sienna? If so, the P3 will perfectly fit into the little compartment under the thumbwheels for the seat heaters. I ran my harness up there and it's a perfect location for the controller when it's in use. When not, I pop off the wires and stow it in the lowest flip-out compartment, so it's always handy (i.e. never gets lost) but only around when I'm using it. Plus, no clampy things to bang my knees on (I am prone to doing so, for some odd reason.)
