It just so happens I set my water system up the way I mentioned above, but not for the same reason..... But for simplicity of design.
When I started thinking about the question, I realized my setup would work as I described.
The problem of low pressure in a park is going to be manifest in low flow. When I thought of this it occurred to me that putting the pump in line as a booster wouldn't solve the problem. (Pumps don't pull suction well and even if they did a strong suction would just collapse the feeder hose)
While my solution above does draw on the tank, it would under some conditions draw slower than if all of the water were taken from the tank so longer showers might be possible.
I like long showers!
There are A LOT of variables here though. For example, a 1" line at 20 psi will flow more water than a 3/8 line at 90 psi...... Add to the equation bottle necks, low flow shower heads, pressure differentials, flow differentials, wow, lots and lots of variables.