Sunncamp Scenic Plus Caravan Porch awning
Sunncamp Ultima (come in several sizes from porch to full)
You will find that due to the height and width of a Dandy Destiny when erected many smaller light-weight awnings will fit with an awning rail. There are lots of porch awnings similar to those above that would look great and give you some door protection and somewhere to store your muddy wellies and other bits and bobs.
Remember that to do this you will be adding an awning rail that was not fitted by Dandy and I do wonder if there was a reason for this such as Water getting into the awning running down the outside of the Dandy wall as its not a solid structure. There could also be other reasons as it is a solid metal rail and could possibly (over a period of time) cause wear on anything inclucing pvc resting on it when folded due to slight movements when in transit. Dandys were very well thought out and I am sure that if there was a reason for the way a Dandy awning fits then it was a good one.