Good advice on the 'gas' side of the water heater.
And be sure the water heater is full of water (turn on both hot and cold until you get a solid stream with no air).
If you stand outside near the water heater, you'll hear the 'roar' when the heater is on. It will take a while (never timed it, maybe 10-15 minutes?) for the water to heat water in the tank and then take a while for hot water to flow out of the tap.
If you hear the 'roar' of the water heater heating, try the cold water side, too. A member on this forum said his water lines were switched; hot out of the 'cold' side.
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.