It could be that a previous owner put a standard household high flow shower head in your shower. The reduced water flow in the trailer, designed to conserve water use, just doesn't have enough flow (volume per minute) to fill and pressurize a high flow shower head. It may feel like a lot of pressure when coming out of the fairly narrow pipe that goes into the shower, but that would be because the size of that opening is less than the total of all the little holes in your shower head.
Try a test using a bucket and a helper with a stopwatch. Try to capture all the water that flows out over, say, 5 seconds, as precisely as you can time it, and see how much of a difference there is. Does more water come out of the shower head when it's attached to the hose than comes out of the shower pipe without the hose in the exact same amount of time?
If the plumbing to your shower head is fairly small, which wouldn't be surprising in a trailer where water is limited, there won't be as much water coming out as there is from the hose with the shower head on it. But if the opening in the shower is also fairly small (without the shower head hose), it might feel like a lot of pressure.
The answer could be as simple as putting in a low flow shower head that is designed to give you more squirt with less water.
That's my guess, at least. Others will probably pipe in with other ideas.