Sorry for your troubles...another dealer failing the buyer
Time to call the factory...they should ship you the manual directly:
If my RV was new and I had problems, I would always communicate with the factory - Just to ensure the dealer was being honest about my case (which often they are not - warranty work is not paid at the retail rate).
These Super C's have an extended fuel filler pipe.
This pipe and the associated fuel vent tube MUST be straight and free of kinks.
In one case here, an owner found after a few trips the fuel filler vent line had drooped and was full of fuel. This prevented fuel from being able to freely flow into the tank at any quantity because air was rushing out of the tank thru the main pipe instead of the vent.
These fuel systems are sealed for emissions considerations, so there is no slack for fuel vapors to escape any other way.
I would check that as the cause...straight and free of turns...plus the smaller vent tube must be higher than the filler pipe and also straight and free of any kinks.
Hope that helps.