There are write-ups online for just this. The more 300-like install has you replace two flat retainers on the floor just outside of the spare tire cover with the rings and then use the grocery bag hooks for the top. (Or if you don't have those hooks, install the second set of rings where those rings would go.
An alternative has you use a hole that's covered by the carpet but basically where the taillight panel and truck side panel meet. Remove the carpet from the side of the trunk and you'll see all sorts of options.
300-Style Mounting:
Custom lower location; should work with OEM rings:
Taillight retainer mounting:
The rings are similar to a christmas tree. Not much to them. There are several retainers you can replace that should work well.
The East/Exit Entry feature is hidden in the Memory Seat Module (MSM) menu in the PCM. It can be turned on or off via the WiTech scanner only. (It can't be selected easily like it is in a Charger or 300.)
Challenger automatic easy entry/exit feature enabled (at https://www.hellcat.org/threads/challenger-automatic-easy-entry-exit-feature-enabled.125041/ )
Tazor's scanner/programmer also seems to have recently added this, but that's aftermarket.