When you say the water heater "fires up" that would be propane, and has nothing to do with plugging in, as the water heater runs off of battery and propane. It may be electric also, but save that for later.
You didn't say new or used on the camper. Does the stove work, will the furnace come om on and heat? Are you getting propane to all of the camper?
If new, are you sure the water heater is full of water,(open pop off valve). May be in winterize mode. Do search on hear for water heater, and you'll learn a lot.
And WELCOME to the forums.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT