Unfortunantly dirt and crud in the gas tank can be a source of problems for this vintage of RV. Short of dropping the gas tanks, cleaning them out, and resealing them, you can only keep the gas filters cleaned out. It does mean stopping frequently and cleaning the gas filters. I use the clear gas filters with replacebale/cleanable elements so you can see their condition (available in the hot rod section of almost every auto supply)
Using one up by the carburator allows you to see if it is dirty and if gas is getting to the carburator. I have seen people replace filters every 100 miles do to dirty gas tanks.
Sometimes the sock on the end of the pickup tube in the gas tank gets clogged up not allowing gas to flow in the lines. The result is a clear filter at the carb that will not have gas visible in it.
The rubber lines used to connect the steel fuel lines to the the gas tank, connect to the tank sellect switch, and connect to the inlet side of the fuel pump can be become old and cracked. When this happens, the fuel pump is sucking air rather than gas. Again the result is a clear filter at the carb that will not have gas visible in it.
Other than a defective fuel pump, about the only other thing a "no gas to the carb" condition can be is either clogged steel fuel lines or a vaporlock condition (engine or exhaust pipe heat vaporizes the fuel in the line resulting in a clear filter at the carb that will not have gas visible in it).
If your Kings Highway is based on the GM P30 chassis with a 454 engine, then the gas tank is in the rear of the chassis. Many people add an electric fuel pump back by the gas tank to push the gas up to the mechanical fuel pump in order to overcome potential vaporlock problems. The tanks are up forward on a Dodge chassis and typically do not need the electrical fuel pump.
Sometimes a previous owner will replace the original veneted gas caps with unvented ones. As gas is used up in the tank, air has to replaced the void where the gas originally was. An unvented cap will not allow air back in the tank (you can hear air rush into the tank when you open the gas cap) and after a few dozen miles the fuel pump cannot pull a suction on the gas in the tank. Loosen caps to keep going but replace them if this is the case.
Take the time to check the entire fuel system as age has a way of creating frustrating problems with it. I replaced the plumping in my entire fuel system due to problems like these.