As if all of the foregoing wasn't enough, a discussion that sprang up around the overall efforts also mentioned the benefits of blocking off heat-robbing airflow through the radiator and thence around the engine. Obviously, a strong flow through the engine compartment at highway speed is going to wash a lot of heat away under the car, and since the whole idea here is to hold the HEAT in the HEAT ENGINE where it belongs, keeping the cold air out of there totally makes sense. The engine block presents nontrivial radiative surface area, for which there's no thermostat controlling rate of heat transfer. Some people have gone to extremes of packing wads of fiberglass insulation all in around the engine to keep it cozy. I figure just getting the highway airflow somewhat under control helps a bit... After looking critically at the grille construction and the relationship with where the radiator and engine-room opening sit, it's pretty clear that the top "smiley" opening is pretty useless, so I've used two pieces of Coroplast to completely close it. They're tied through punched holes and then around the plastic struts, and flex very nicely up against the edges of the opening inside. It's yellow because I'm reusing signage from the 2006 Ipswich renewable energy festival. The stuff cuts easily, it's fairly strong and weatherproof, and was in near-to-hand cache in the house. The ends of the ties are then taped down to prevent them from flapping around; this part is semi-permanent and may not even come off for summer since it possibly helps a little more air go up and over the car too. Since the whole nose of the car is plastic, I'm not worried about trapping moisture or pulling up paint.
The lower opening is much larger and is pretty clearly where most of the air comes in. It probably circulates quite a bit in the large space in the nose before heading through the radiator; however, one must remember that the section of radiator that handles inverter coolant is at the bottom of the assembly. It therefore seems sensible that if any part of this is going to have an easily-changeable option, especially when planning a road-trip to warmer climates, it should be the lower part. So this is one large piece, mounted on loose loops of tie-line at the lower corners and with a long piece near the top that allows it to flop completely back and allow full airflow in to the radiator.
When pulled up and tied more tightly, though, it closes off the center part of the lower-opening grille but leaves the very outer sections [which are physically separate plastic inserts anyways] open. These are not directly in front of the radiator but have little angled plastic deflectors behind them to send the air more or less inward; I figure I'll leave these open for enough airflow to handle minimal cooling needs for the inverter and the main radiator. I wouldn't really expect a high load in cold weather, but any engine will get plenty warm when climbing a long hill so *some* cooling capacity needs to be left in. It's just out of the direct oncoming blast at highway speeds now.
The assembled whole gives the car a new oddly aggressive aspect, or maybe it's just the camera angle... still, warmup time and heat-holding does seem to be improved after highly sophisticated technical testing [i.e. drive for a while with an eyeball on ECT and IAT via OBDII, get out, feel around under the hood] without undue heating of any components. This rig even went out in full cold-weather mode on a freakishly balmy 65F day in November, although after seeing intake temps climb up toward 170F I stopped and took the WAI hose off the airbox for the rest of that particular day's run. Let it snow!