Somewhere there may be a high point in the system that has air in it... possibly a shower head. Find it and run all the air out.
Also the fresh water tank can get air trapped in it by sloshing around during towing.... but not that much.
Possibly the uptake side of the water pump (if it's in use) has an air leak and is sucking air in along with the water.
Single empty-nester in Middle TN, sometimes with a friend or grandchild on board