Hello all. On my airstream TT, being it has a curved side wall, the coils at the bottom are almost 6 inches away from the wall at the bottom input vent and about an inch or so at the top roof vent. I did what Enochlight suggested about 15 years ago after talking to a dometic service rep. The alum sheet was bent at about a 45 degree angle upwards and was in far enough to be about 1 inch from the coils and was attached to the inside wall at the upper edge of the lower vent. Even without a fan that made a world of difference.
Happy camping nm1oqrz