Since this is an electric tank and you have a crawl space you can-
1- Flip the breaker to turn the heater off
2- Plumb the house so there is a master water shut off (You already have that) and 2 more drain lines with shut offs; one for the cold water pipes in the house and the second for the hot water tank. When you leave, turn off the house valve and open the other 2 valves. Everything will drain by itself.