This may be of use. I saw this ad on eBay yesterday [You must be registered and logged in to see this link.]
and I was reminded that a lot of Conways are the same size as Dandys. Admittedly this is one of the larger ones.
Dimensions for Conways can be found at [You must be registered and logged in to see this link.]
and selecting option 12 Conway trailer tent sizes.
I'm sure one will match up to you.
The downside: There isn't a full tent frame ad the poles are meant to attach in a different manner so new pole ends would have to me sorted to provide the u section to fold ove the Dandy wall. This has been done by others and the ends could be supplied by Riva if your not practical on metal bending.
A zip would need to be sewn into the Dandy, or a Piece of PVC that then mimicked the flap that attaches an awning on a Dandy. I'm not sue what Conway do for the flaps that seal off the under bed areas.
Have you seen what Conway awnings go for? Often for nowt and there are a lot more Conway awnings than Dandy awnings about: [You must be registered and logged in to see this link.]
Hope this might inspire you or someone else.