Motorhome Water Pumps

I know there is another recent thread on problems with water pumps but this is a slightly different question if anyone can help.

On my previous motorhome, which had an underslung water tank the pump was under the bed attached to the floor. On my new motorhome which has an internal water tank but fitted with a submersible Whale water pump with an external pressure switch. What I find is that the shower pressure is pretty low compare to the first motorhome and I wondered if it was possible to swap the submersible pump for a heavier duty external (to tank) pump and would it achieve my aim? 

Picture below shows position of tank and pressure switch.

David