If you have a split system Herron Air command or similar and have an unexplained draught whistling around, have a look at where the two white insulated pipes enter and exit the van. Ours had a 'mistake hole " of 50mm, plus the one they used drilled through bottom of cupboard wall next to rear of unit. A clear path for breeze and wind , as no sealant used in void areas. I removed the outside cover, 14 screws, and filled all gaps today. Hopefully sorted.