Vapor lock is simply the fuel in the line getting hot enough to convert to a gaseous state either just before or just after entering the carb. The fuel is there, but not in a usable quantity. Choking draws additional fuel into the carb, removing the issue. Look to see if there is a way to let cool air circulate near the fuel lines and carb after landing. A good check to see if that's the problem would be to do as you noted and remove the cowl for a flight to see if the problem continues.