Persistent squirrel, that's for sure !!! There are a couple of online parts catalogs available that you can use to get part numbers for what you need. Armed with those part numbers, often times a Google search will provide you with some alternatives for cheaper prices. Just do a search for each part number individually and you should find who has them cheapest. Here is one catalog link:
http://www.rvdealership.com/rvdstore...rNumber=885555
If you can't find your actual A/C listed in the left column, you can type in your unit part number to locate the parts breakdown you need.
Since it's apparent the OEM top cover isn't going to keep the critters out, you might want to consider the MAXX AIR after market shroud. They are usually more durable and offer better ventilation than the factory "top-side cover".
Good Luck !!!
ADDED: I found this on the Dometic site: "You can order parts for your Dometic RV product(s) directly by calling the retail sales department at 1-800-544-4881. Please be sure to have your model number available so the correct parts list can be obtained. If you are in need of any Dometic RV refrigerator, air conditioner or A&E awning parts you can also call us at 1-800-544-4881 or purchase from any RV Dealer or Camping World location."