When we bought our trailer I found that on each side of the bed towards the front there were open areas, which was letting in cold air. I built some L shaped brackets and filled the space in and it stopped a lot of the cold air. The only way we found the open area was to move the mattress. Hope this helps.
2011 jayco 33rlds, 2002 Ford excursion, v-10, 3:73 gears 4x4 mine. 2008 Suzuki sx-4, hers. Retired Air Force, now Retired.