Measuring electricity use

I second the Kill A Watt meter if your overall draw will be moderate. They're only good for about 15 or 18 amps. If you want to measure the draw using the 30 amp or 50 amp connection you will need to hard wire in a kWh meter. I've done that at my house on my electric water heater circuit. I wanted to see how much it contributed to my electric bill.
kWh meters (and sockets to hold them) might be hard to find at a store. The power company might be willing to give or sell you one. I'm a dealer for AEE Solar who sells them but they will only sell to their dealer network.