Check your basement compartments.

Check under the hood, but maybe hard to locate if it has a cover over it. You might be better off to look in that area from underneath. You are looking for a tank, about 5-6 inches in diameter and about 18 inches tall with a drain plug on the bottom. The filler cap will be on top accessed from under the hood.

on my 08 journey it is under the front steps, alarms will go off if only a half of cup low

You shouldn't have to go under the coach. They have it in an assessable area.

I don't have a Monaco but my hydraulics are in a basement bay and the tank is a black metal box at the right front of the bay. Fill plug is a round knurled knob.

Not sure on yours but check on the passenger's rear side engine access. On our 01 Spartan chassis, it is located on the forward side in that compartment.