I have completely sealed up my 1181 through the floor only. I removed the bottom because of a spongy floor and there was not a ton of insulation down there. The walls are about an inch thick and the windows are double pane gas. The interior is very warm and tight once you cover both the exhaust fans, shower sky light and escape hatch. The door is very solid but cold around the glass. I cover that too. If you wondering about the soft floor it was due to a broken aluminum weld that was easily repaired with some angle iron and SS nuts and bolts.