Hi Reg and Pat,
1994 you will have a Cascade 2. At that time most Cascades were gas only, and the electric elements were only just coming into fashion. How will you know which you have? Well the simplest thing is to look at the heater in the bed locker. If it has a white plastic housing attached to the end of the tank at the inboard end, you have a Cascade 2 GE with the electric mains element.
Follow the power cable from the housing and you should find a it connects into a domestic type fused spur with switch, usually on the kick board or end of the bed locker. Provided the heater is full of water - which yours is because you water flow from the hot taps, you just need to switch the power onto the element. the element is thermostatically controlled so you can virtually forget it whilst on holiday.
If you don't have the white plastic box then its gas only. Make sure the gas supply is turned on to the heater, and the flip the switch on the beige controller.
If its working, then you will hear a clunk as the gas valve opens followed by the sound of the spark generator and may be a slight plop as the gas ignites. When the heater normally works it might only give one spark which lights the gas almost instantly. Again the gas side is thermostatically controlled, so you can leave it running all day and night if you wish, or just turn it on half an hour before you need it.
You can use gas and mains heating together to heat water more rapidly - but it will still take 15 to 20 mins to get hot water
As with all gas appliances, it may need a service which should be left to a competent gas fitter.
To get hot water out, you have to push cold water in to displace the hot, so it never runs dry even if your water barrel empties. Because of this it is important to remove the drain plug to empty the tank of water before travelling and when storing when conditions are likely to freeze.
I suggest you look at the following website where you can see and download a copy of the instruction manuals for many Carver Cascade Rapide which is a slightly updated model, but the same basic operating instructions apply except that the operation and lights of the control switch are different.
http://www.arcsystems.biz/