Hello Ian,
The simple answer is yes, however life isn't always that simple. The flow capacity of a pump is not always an indicator of the pressure it will develop, and the pressure in the caravan may be limited by the method used to control the pump.
If you have a pressure switched system, then a 'bigger' pump is unlikely to make much difference, as the operating point of the pressure switch limits the maximum pressure developed. You can try adjusting the pressure switch, and you may find that your existing pump is actually all you need.
The other method of controlling the pump, is by switched taps. Basically all the taps in the caravan have a micro-switch buried in them, and as soon as you turn the faucet the pump begins to run. In this system a more powerful pump may make a difference, but the limiting factor is usually the bore of the pipe-work and the internal openings in the taps.
Another consideration will be the amount of water you use. Your water heater will only have a limited volume of hot water, and a higher pressure/flow will use it up more quickly. Also you will need to fill your supply tank, and empty your waste more often.
Caravan showers were never designed to be perfect replacements for a domestic system, but they do at least allow of an element of freedom from site washroom blocks.