My coach is not a Holiday Rambler. Mine is a 2001 Alpine Coach 38FDDS. I suspect the componets are similar if not the same. The Hydromax system provides boost for both the brakes and the power steering. The hydraulic pump is in th engine bay.Everything else is under the floorboard below the driver's feet. The fuses for my coach are located on the bulkhead near the steerigh box/brake booster equipment. This same hydraulic system also powers my radiator fan.
Your thread might go better is you say what kind of trouble you are having.
Here is a photo of the booster: