WE OWN A 2013 KEYSTONE COUGAR 5TH WHEEL MODEL 331MKS. ON 4/4/14 WE WERE AT A CAMPGROUND AND STARTED TO SET UP. THE RIG WAS ONLY ON 12V BATTERY POWER. I HAD NOT YET CONNECTED TO SHORE POWER. WHEN I PUSHED THE BUTTON TO LOWER THE LANDING GEAR, NOTHING HAPPENED. I TRIED THE REMOTE CONTROL, AND NOTHING HAPPENED AGAIN. I WENT TO GET THE POWER CORD INTENDING TO PLUG IT IN. THE CORD WAS IN THE STORAGE AREA IN THE FRONT, UNDER THE HITCH, WHERE THE BATTERY IS. WHEN I OPENED THE DOOR, IMMEDIATELY SMOKE WAS BILLOWING OUT. THEN I SAW THE FLAME. IT WAS COMING FROM THE CIRCUIT BOARD ABOVE THE BATTERY.I IMMEDIATELY GOT THE FIRE EXTINGUISHER. AFTER USING IT SEVERAL TIMES, THE FLAME KEPT COMING BACK. I CALLED 911 FOR THE FIRE DEPARTMENT. THE PROPANE TANKS ARE RIGHT NEXT TO THE AREA BURNING. I IMMEDIATELY REMOVED BOTH OF THEM. ALL I COULD THINK OF WAS THE POSSIBILITY OF AN EXPLOSION. THE DISPATCHER ASKED IF THERE WAS ANYTHING ELSE NEARBY THAT COULD BURN. I SAID "YES, IT IS CONNECTED TO MY TRUCK WHICH IS FULL OF DIESEL." I COULD IMAGINE EVERYTHING GOING UP IN SMOKE. I TURNED OFF THE BATTERY, TURNED OFF ALL THE CIRCUIT BREAKERS, BUT THE FLAME KEPT COMING BACK AFTER I KEPT USING THE FIRE EXTINGUISHER.MY WIFE WENT FOR THE CAMPGROUND RANGER. I FINALLY EMPTIED THE FIRE EXTINGUISHER AND THE FLAME CAME BACK. I HAD NOTHING ELSE TO TRY, SO I REACHED IN AND PULLED THE WIRES OUT WHICH WERE ALL MELTED AT AND AROUND THE CIRCUIT BOARD. THE CAMP RANGER TOLD US THAT HE HAD NEVER SEEN ANYTHING LIKE THIS BEFORE