I have the older model ARB Fridge (like the Engel) and am looking for a travel cover, new or used. Hit me with a PM if you have one you no longer need.
An inexpensive way to make a cover (until you get a matched fit-one), is to use Reflectix insulation. Should be ~$25 for a 2' X 25' roll (it tapes together very well). The 4' which I used is more $$.
The one I made for the engel I recently sold took just a minute to fold into place. Seemed to work pretty well.