You have 3 problems.
1. Water should NOT leak between the awning rail mount to the upper sidewall roof. I doubt it is leaking BEHIND the awning rail. The roof material over laps the top corner and they do use Butyl sealant behind the awning rail. The usual cause of leak at the awning rail mount is the area where the awning rail is spliced. The awning rails rarely are 1 piece and there are 2 sections. I hope the awning WAS retracted in that torrential downpour.
2. The outside doors and partitions and covers should NEVER leak. Your compartment door should not
3. The furnace vent should NOT leak. Are you POSITIVE the water came in thru the furnace outside vent? Is there a Refer access door in the vicinity of that furnace vent? Was the rain blowing into the side of the RV where that furnace vent is located? IF SO, I can see where it would leak. Take the refer outside access door off and see if the area behind the refer is wet if on same side as the furnace vent. Doug
PS I just looked and saw you have a new Tiffin. WHICH awning do you have the Girrard or Carefree.