If your dealer's parts department doesn't have the information and parts you need, or doesn't seem helpful, try this website:
http://www.trekwood.com/replacements/4285/Seal
There you'll find diagrams of all the 2008 Challenger rubber seals and pricing for each. While Trekwood is "expensive" as compared to some suppliers, I've always found the parts I need on their website. Then, using their part numbers/names/descriptions, I've often been able to search the internet for less expensive alternative sources.
Good Luck.