FYI I completed my installation today. Some highlights...
1. I decided to place the head unit under the driver's seat. This was done in part because the Icom IC-208H microphone cable attaches to the head unit, not the detachable faceplate. The mic cable comes out from under the seat and has enough length to be usable.
2. Power and antenna cables are routed in the wiring trough under the door thresholds, back into the trunk. All the wiring is behind the left-hand side trim panel inside the trunk, the antenna wire follows the bundle that goes along the left hand trunk hinge. The (fused) power leads are connected directly to the 12v battery.
3. The remote-head control wire goes up the side to the trim piece below the fuse box on the side of the dash, then snakes alongside the steering column to the faceplate which I mounted above the steering wheel on the dash.
4. The antenna is a Radiall-Larsen trunk-lip mount "TLP" series attached on the left-hand side of the trunk just ahead of the spoiler. I trimmed the body putty Toyota uses on the trunk lip to get metal to metal contact for the antenna. I have not yet bonded the trunk lid to the body, but I will be doing that to improve the ground plane.
So far, no problems, the airbags didn't go off when I hit transmit, so I think it's going to work OK.
Steve