On my 2003 Monaco Dynasty the high and low pressure ports were in the rear (engine compartment) - near the a/c compressor. I had to un-latch the air filter and move it to the side slightly to reach the fittings. The only correct way to fill, is to evacuate the system, hold the vacuum for at least an hour, and then add the amount of coolant (R134a) called for. Mine calls for 4 lbs. Depends on the length of the MH and other factors. The amount should be in your owner's manual or a sticker near the ports.
You can use a pressure/ambient temperature chart to compare high and low pressures in the system to get close to the correct fill.
2003 Monaco Dynasty Jack (39', Cummings ISL, tag axle)
2015 Thor Hurricane (28K)