The Adco cover that we had on our 19 fits our 21 perfectly.
So depending on the brand and fit of the cover you have there's a possibility that it might also fit a 21, in case anyone near you with a 21 is interested in a cover.
Sometimes there's a bit of confusion on the size of the trailer with some measuring the actual shell and some measuring bumper to hitch.
When it comes to covers it's nice to know if someone else with the same size has used a particular type and how it fits. In this case it'd probably fit a 21 shell just fine but maybe not right up to the hitch.
The trailer is new to me, it came up for sale just an hour’s drive away, a rare thing as I’ve been looking for an Escape for a while. I’m not planning on using the cover as I have a garage that will allow me to store the trailer, once I get ride of a lot of ‘good stuff’!!