Our Durango is only the R/T version (5.7L Hemi), as it's my wife's daily driver and I couldn't talk her into anything faster than that. But yeah, on that version there's just an open hole in the bottom cover, which I reach up thru to access the oil filter. Like you, I kinda wondered if there should be a door hatch there, but there's no provisions for attachment if there were one, so I guess that's just supposed to stay open.
I personally hate it. I like the removable pan of the SRT much better. Four 10mm screws, I can have it off in about 10 seconds, and then everything is wide open. The Durango is almost as bad as the RAM, in terms of making a mess while removing the oil filter.
On the RAM, I've actually taken to hammering an awl thru the bottom of the filter to drain it, before removing. Otherwise you end up soaking the 4wd solenoids and front axle components with motor oil, just to have it drip in the driveway for the next two days.