DECEMBER 26, 2013, MY WIFE AND I STOPPED AT A REST STOP IN VAN HORN, TEXAS FOR A FEW HOURS REST. OUR RV WAS NOT MANUFACTURED WITH A FURNACE AIR RETURN DUCT. WE HAD JUST BOUGHT A NEW DODGE 3500 WITH A CUMMINS DIESEL ENGINE HAVING ALL THE BELLS & WHISTLES (FIRST FOR US). WAKING UP I DECIDE TO SHOW OFF THE (NEW TO US) ENGINE REMOTE START FEATURE. BEFORE THE ENGINE STARTED I WAS PUTTING ON MY SHOES TO WALK OUR PET. WHILE WAITING ON OUR DOG TO RELIEVE HERSELF I HEARD MY WIFE YELLING OUT, EXHAUST IS COMING INSIDE. I DIDN'T HAVE A TRUCK KEY WITH ME SO I RAN TO THE RV TO SHUT OFF THE PROPANE FUEL FURNACE. THE FURNACE TAKING TIME TO SHUT OFF I STUPIDLY TURNED ON THE LIVING ROOM POWER VENT IN THE CEILING. THIS VERY POWERFUL VENT FAN MADE THIS SITUATION MORE DANGEROUS. UNDER PRESSURE HEARING MY WIFE YELLING I DIDN'T REACT PROPERLY AND BEGAN PRESSING FURNACE BUTTONS WHILE STANDING ON THE STEPS TO BED & BATHROOM ABOVE THE TWO FURNACE AIR RETURN GRILLS I BREATHED A LOT OF THE DIESELS EXHAUST. I CALLED POISON CONTROL FOR MY LUGS WERE BURNING SOMETHING TERRIBLY. KEYSTONE RV MANUFACTURED OUR 5TH WHEEL WITHOUT A FURNACE AIR RETURN DUCT. OPERATING A VENT FAN DRAWS OUTSIDE AIR IN REVERSE DIRECTION THROUGH THE FURNACE TWO WOODEN VENTS LOCATED IN THE STEPS I WAS STANDING ON. WE HAVE NO WAY TO PREVENT OUTSIDE AIR (CONTAINING EXHAUST FUMES OR ANY OTHER HARMFUL PRODUCT PRESENT IN THE AIR) FROM FREE FLOWING INTO RV LIVING QUARTERS WITH FURNACE FAN ON OR OFF. KEYSTONE AND SELLING DEALER REF