Third idea is to let the actors drive the car. By far the easiest way to go, but not the safest. Also, they have to be focused on driving the car, so their acting might suffer from that.
I suggest you go to U-Haul and rent a “car carrier” to tow behind a pick-up truck. A number of commercial productions I have worked on have done this with great success.
I don’t recommend that you try to power lights with an inverter through the lighter socket. Car lighter sockets are only capable of handling a couple of hundred Watts at most and you usually require at least a 400W HMI to provide fill during a day lit shoot. To run a small HMI you can use a "Battverter" - which is a Battery/Inverter system. A "Battverter" system consists of a 12V DC power source (usually Marine Cells), a DC-to–AC True Sine Wave Power Inverter, and a Battery Charger. Wire these components into a Road Case or milk crate and you can put it on the floor in the back of the car.
Here are some production stills that show you two Battverter systems I built to run lights in vehicles at various times. The first is a 750W "Battverter" rig wired into in Calzone case.
To maximize the running time on the batteries, I made up a "jumper cable" that we attached to the leads of the pickup truck's battery. That way the engine alternator charged the batteries as they were being discharged by the light. Tie–ing the Battverter into a vehicle engine will extend the running time on your Battverter batteries so much that they may never run out of power.
The production stills below show a more elaborate 1800W Battverter system that we built to run 16 - 4’ kinos tubes inside the airport shuttle bus. Use this link for details on how we wired it into the shuttle bus.
(Kino Flo 4x4s rigged to an exo-skeletal frame of a Shuttle Bus and powered by an 1800W Battverter)
If you don’t require a lot of light, a Battverter will even enable you to use a car engine as a generator. Use the engine to run the lights through the Battverter as described above during set up and rehearsals. When it comes time to shoot a take, simply shut off the engine and continue to run the lights on the Battverter alone. Running the vehicle engine between takes charges the batteries so that they will run lights all night.
(Custom 1800W BattVerter powers 16 - 4' Kino Flo single tubes rigged
in the interior and on the exterior of an Airport Shuttle)
When building these rigs, keep in mind that when voltage goes down, amperage goes up. Wire that carries 12V DC has to be much larger than that which carries the same load at 120V AC. For instance to supply 12 volts to the 1800W inverter used on the shuttle bus required that we run 2 ought feeder to the buses' alternator. Also be sure that the alternator is large enough to take the load without burning out.
Finally, You have to be really careful when choosing a DC-to-AC inverter for film production because there are three basic types of inverters and not all of them are suitable for all types of motion picture lights. For more information on what type of inverters to use with different type of lights I would suggest you read an article I wrote about portable generators that is available online at http://www.screenlightandgrip.com/html/emailnewsletter_generators.html. Since inverter generators use the same three types of inverters, the information in the article is applicable to stand alone DC-to-AC inverters designed for use with batteries as well.
If you don’t want to tie batteries into the car’s alternator, you should consider using a small portable generator. But, you don’t want to use a generator, like the Honda 2000, that has a gravity feed for fuel. The fuel sloshes around and causes the generator to run erratically. I suggest you instead use a generator that has an electric fuel pump like our 7500W modified Honda EU6500is Inverter Generator. The fuel pump assures that not only will the engine receive a continuous feed of gas, but also that it won’t run out of gas in the course of a production day. The EU6500 is so quiet that you will not hear it in the car with the windows closed and, as you can see from the picture below of another rig, it is cable of powering large HMIs for daylight fill.
A 7500W modified Honda EU6500 powering a couple of 2.5HMI Pars on a car rig.
If you have any questions about using inverters or generators, I would suggest you read an article I wrote on the use of portable generators in motion picture production. Harry Box, author of “The Set Lighting Technician’s Handbook” has cited my article in the just released Fourth Edition of the handbook. In addition, he has established a link to it from the companion website for the Fourth Edition of the Handbook, called “Box Book Extras.”
Of the article Harry Box states:
"Great work!... this is the kind of thing I think very few technician's ever get to see, and as a result many people have absolutely no idea why things stop working."
"Following the prescriptions contained in this article enables the operation of bigger lights, or more smaller lights, on portable generators than has ever been possible before."
If you haven't yet read the article, or looked at it in a while, it is worth reading. I have greatly expanded it to be the definitive resource on portable power generation for motion picture production. Use this link to read it on-line for free.
Guy Holt, Gaffer, SceenLight & Grip, Lighting and Grip Rental & Sales in Boston.