Some DP with air brakes and suspension have a connection in a storage compartment or in front under the windshield for a place for a tow truck to use their on board compressor to keep suspension and air pressure up while towing. Some RVs can use this as a connection point for an air hose, others have a one way valve so it only allows air in, not out.
Since you have to run the main engine to keep the air pressure up, many have found a small pancake air compressor is faster, easier, and quieter. Just be sure to get one that has 125 psi capacity.
If you do find you have an air connection, this video shows you how to make an inflator to use instead of having to have someone in the driver's seat repeatedly pressing the brake treadle to keep compressor at +125 psi.