Cobra, Tripp-Lite, Aims, Xantrex. All are good inverters. Modified sine wave inverters are cheaper, like a 2000 Watt one will run you in the $150-$200 range. A pure sine wave will run two to four times that.
If you plan on running a microwave for a few minutes here and there, a 1500 Watt inverter will do. If you want to run the microwave and lights and a TV and other stuff you haven't thought of yet go with 2000 Watts.
If you want to run a ceramic heater, plan on having a ton of batteries (close to it, anyway). That or being really cold most of the time. A small ceramic heater won't keep a cargo van warm. It'll barely take the chill out, provided you have the van extremely well insulated. Depending on the setting of the heater, 1500 Watts or 1000 Watts, it will draw 12.5 amps or 8.3 amps, respectively. But that's at 120 volts. At 12 volts though an inverter you need to multiply that by 10, or 125 amps at 1500 Watts and 83 amps at 1000 Watts. (There's also an additional 10% loss in the inverter during the inversion process).
If you have, for example, one of the Wal Mart Everstart Max marine deep cycle batteries at 125 amp hours, at a 125 amp draw the heater will run for a little less than 45 minutes before you run the battery dead, dead, dead, or about an hour before you run the battery down to 50%. Every time you run the battery down below 50% you will significantly shorten the life of the battery.
A microwave isn't good for a battery, but then again you're not running it for extended periods of time. A few minutes here and there isn't that big a deal. But any resistive heat appliance, like a heater, a 110 volt air conditioner, a dish washer, clothes dryer, those are not well suited at all for 12 volt operations. A 110/120 volt electric heater simply will not come close, not even in the ballpark, to what you need a heater to do out here in a cargo van.
Then again, if you have 2000 amp hours of batteries, which will be roughly 1400 pounds of them (16 Wal Mart batteries), you can run an electric heater quite well for a good 8 hours before you hit the 50% depth of discharge mark. And if you want to do it right, that means 10 of the 6-volt high end AGM deep cycle batteries from Discover-Energy or Concord, at about $500 a pop. That's five grand for batteries, plus another $500 to $1000 for battery cable and specialy cable lugs and all the fuses and getting them all set up to be properly monitored with a battery monitor.
Or, you could use a 1500 Watt inverter for the TV, laptop and lights, a single Wal Mart battery and a simple isolator or battery separator to keep it charged up. To keep warm, pony up the $1500 or so for an Espar heater that will us about a gallon of fuel every 12-15 hours.
