tailgate seal gasket

This might sound goofy for typical pick-up bed use, but I mostly use mine to store things under the lockable, roll-up tonneau. The only complaint I have (& it is a real bitch!) is when going down dirt roads. You can just about guarantee that anything in the bed under the tonneau is going to be...

I just put a BakFlip on my RL and took a hunting trip on some gravel roads. Got lots of dust in the bed and I don't like that. What are my (our) best options for sealing the tailgate? Anything OEM or aftermarket that has worked especially well for you? Thanks in advance for the advice! John