Jump on them for that price! You don't need to cut the doors, you just need to make a baffle. They're only 3" deep, and the cutout is just a hair over 7.75 inches. You have 2.25 inches before you hit the window. I'd go with 1" starboard (HDPE) for the baffle.
You will need to trim off that thin plastic oval on the backside of the door panel with a razor knife or dremel tool though. And the MW182's will absolutely demand that you cover all 3 of the big holes that you'll find in the Sienna door. Deaden everything in the doors as well. I used about 20 ft2 of deadener on each of my doors and a yard of Ensolite on each door.
This is the finished deadening I did before my install, which is still in-progress. All the holes are covered with hardboard, wrapped with deadener (a mix of BXT II and Stinger roadkill pro). Door release and lock cables are wrapped in Ensolite, then covered with 1/2" flex-loom, then that is sandwiched in the deadener and Ensolite so that it won't bind up.
Do. Not. Cover. The. Sensor. With. The. Yellow. Plug! It's in the bottom outer corner of each door. That's part of the STAR airbag system. It looks to be an accelerometer.
Oh, and when you cover the holes, your door panel won't fit until you take a flush-cut dremel (one of those vibrating tools) and cut the white plastic honeycomb piece so that it's all flush with the lowest layer. You'll know what I'm talking about when you see it.
To the OP, sorry we heavily hijacked your thread!