A general rule of thumb is 1 watt for every 1 AH of the battery. While this is not necessarily true for every case, it is a good starting point. A better measure of power is a watt (thats why the power companies charge you by watt hour or Kilowatt hour.)<br /><br />A 15 watt solar...
Always always ALWAYS install a fuse as close as you can to any wires coming of the positive terminal of a battery. All it takes is for a crimp connection to come off while you are moving and the wire touching the frame, and you are on the side of the road with your trailer/car on fire.
Running a 200W heater will suck your batteries dry pretty fast, no matter what type of charging mechanism you use. Granted, in such a small space as a van you will not leave it on for that long because it will get very hot. Have you ever thought about a Mr. Heater Little Buddy...
I suggest you read this blog in it's entirety. Its long but will save you hundreds if not thousands of dollars. I used his insights and experience to install a solar array on my Teardrop trailer, it charges the battery better than the built in charger does (and A LOT faster).<br...
I can't speak to a Crown Vic, but I modified my 2005 Honda Pilot into a camper. I removed the rear seats and built a wooden platform to fill the hole and provide a sleeping area. I added an upper shelf area to the platform for shelving/storage, modeled it after our Little Guy 5x5...