People tend to think of a cover as if it were a rigid box, like a cigar box, that drops down over the trailer. And they worry that if the box is only 18 feet long, and the trailer is 20 feet long, the box won't drop. That is not a good way to think of it, because the cover is more like a bag than a box. If the cover is 18 feet long for a 20 foot trailer, but the cover is also 10 feet wide and the trailer is 8 feet wide, then the extra 2 feet in the width dimension will wrap around and cover the needed 2 feet in the length dimension. The only effect is that the corner seams in the cover don't fall exactly on the corners of the trailer. But that really doesn't matter, as long as the trailer is covered.
You can find several discussions and a lot of info by using the Search tool on the term "
ADCO" (the manufacturer of a line of covers). For example, take a look at Post #6 in this discussion.
http://www.trailmanorowners.com/foru...ead.php?t=2046 An
ADCO 12295 works quite well for us.
Bill