Can you do it by yourself reasonably easily?
I prefer having a helper, but in a pinch, one person could do it.
Need pic of how this works with diff.
I picked up a funnel at a local "Advance Auto" parts store. It has a valve at the base of the funnel, hose, and a tip on the end of the hose with a cap. There are some holes with plastic plugs in the floor of the trunk. Route the hose through one of them and into the diff fill hole. Pour away. I've also gone through the left rear wheel well opening, but that's best done with a helper to make sure the hose doesn't pop out of the diff.
I use the same funnel for the transmission. Go in through the engine bay. Route the hose along the exhaust header/down pipe and into the transmission fill hole.