I route a clear plastic hose out over the passenger wheel and fill it from there. The hose goes to a funnel and I use a bungee hung from my garage door support beams to hold it up. I fill while standing upright.
I'm one of the few who uses a gasket. I also use RTV on each surface to fill slight imperfections.
You'll need a 3/8" drive to loosen the fill plug (do that before you drain the fluid). Wear mechanics gloves and be careful when you break that fill-plug loose - more than one stanger on here has gashed his hand when the plug lets go.
Good luck.