Nice post Todd .. but be advised folks this info must be model year spacific .. I just added a 10 power Highlander front seat to a 2012 XLT cargo version sold in Canada, and found to my disappoiment that this process would not work ..
In my situation the bolt locations did not exist as the extendend cargo area floor plate was not bolted in, but was spot welded .. none of the factory bolt locations were left in place.
To have any way of securing the plate I mounted my seat on, I had to go through the cargo deck floor, and with all the gear that is on the other side, gas tank etc, this takes some planning.
I wanted to reclaim the rear foot well, so I ground out the spot welds and cut out one half of the extention, leaving the other half in place .. be advised in my model year the floor carpet is cut at the beginning of the extention, so you will need to allow for an addition of floor covering in the 8" void the removal of the cargo base extention creates .. the pics above in the other post look like the cargo extention was left in place , this would be leg length spacific ... my mod was for a 6'2" person with long legs, and a Toyota seat ..
I bought my van used for this purpose , and was prepared to go through the cargo floor, had 108k on it, but wanted it for the body, sadly the previous owner did a rather sloppy repair job to a broken third break light, and it was leaking in the cargo area roof .. but that is another story :-)
The rear scuff plate (molded plastic) starts with 3T on the wagons, and 9T on the cargo versions. I have yet to fit the one I received from the dealership today ( 3T replacing 9T ) and will report if it is lacking .. may also need to get a different front piller base to meat up with the 3T scuff plate as in my mind it seems a few inches shorter ...