I have a 30 amp plug so I will use electric heaters on low at each end (set to high the breaker trips) and the gas furnace is a back-up for nightime when the temp dips. Someone else posted this also...but keep in mind, each electric heater that is 1500-2000 watts, draws approx. 12-17 amps. If your plug is a 30 amp...you will max it out with 2 heaters and possibly trip the main...unless the heater has a low setting. The low setting draws fewer amps and could allow you to operate 2 heaters together on low and maybe even 1 of them on high. Set the furnace down low to compensate for when the electric heaters can't keep up.
Bart and Tina
2001 Chevy 2500HD 6.0 Silverado 4x4-Banks Power
1997 Jayco Eagle 5er 285BHS-flipped axles