Your tank heaters, unlike your Water Heater, will be fine operating without any liquid in the tanks. Yes, the Water Heater element WILL burn out if the water heater is empty when the element is turned on. This is because you need water in the hot water tank to absorb the heat of the high energy heater element. The electric heating elements on your "other" tanks are a much different configuration and will be fine even without liquid in these tanks.
Days camping (2016)----181 days
Days camping (2017) --- 82 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi, w/air suspension
30 years RV'ing
11 different RV's