New Casitas come with an accumulator I understand. My 2003 was before that time. The accumlator uses the water pump to build up a reserve of pressure and then when you turn on the faucet, the water pump turns on and off less frequently. Saves battery life (I think Pete had a nice chart that illustrated that) and wear and tear on the water pump. Although water pumps appear to be pretty robust devices as it is.

As a maintenance tip in the spring, part of the recommissioning of the trailer in the spring, you should check the pressure in the accumulator with the water pump off.

I chose the area in the dead space in the corner, but location is pretty flexible and I've seen installations in the front closet as well.

I bought mine at West Marine. Water Pressure Accumulator

The pictures show a step wise installation. I used PEX tubing and PEX connectors. I bought the crimper (at Lowes). It's pricey but I love tools. I expect they'd rent the crimper as well.

The accumulator has worked without issue for three years. I have relatively easy access. If my closet space weren't so limited already I might have chosen there first.

I wish I had an accumulator, as it is a little annoying to have the pump rapidly cycling on and off at low flow rates. I suspect that the variable speed pumps (e.g. SHURflo Extreme) are an even better idea, if the pump is being replaced anyway, although the accumulator would be less expensive if there's nothing wrong with the pump.

I can believe that cycling is bad for energy consumption, since surges of power are needed to start the pump motor); I suspect that it is also bad for any weak points in the plumbing.