30 psi isnt much pressure.... and the trailers that use 1/2" pex pipe water lines have restrictions at almost every connection, elbow, and fitting... because they use so many plastic fittings which only have a 5/16" hole thru them.... and the restrictions add up to cause a low water flow thruout the rv.... the brass PEX fittings have a 3/8" hole, which would be better, but they arent as cheap as the plastic ones... the plastic is GOOD quality, but just cant be cast as thin as the brass fittings can....
to remedy the problem, you will either need higher pressure to compensate for the restrictions........
Or, less restrictions to allow for a higher flow at the same pressure, which can only be achieved by replacing all the fittings with ones that have a larger hole thru them...