Yes, RTV by itself can work just fine- that's how Mopar has been doing it for years. Just make sure you clean the surfaces well.
Personally, I'd just use the cork gasket- they work ok if you're careful with them... not great, but ok. First, make sure the gasket surface on the pan isn't warped- often it'll be pulled in around the bolt holes. I've hammered them flat... that might work for you if you're awesome like I am. But if you're not as awesome as I am, you might mess up the pan. So be careful. Anyhow, I prefer to glue the cork gasket onto the pan with 3M weatherstripping adhesive, and give it some time to set up. Then make sure that the gasket surface on the bottom on the trans case is clean and dry, and don't put ANYTHING else on the gasket (Putting RTV on it will just facilitate its squishing out). Install the pan and don't tighten the bolts too tight- just snug them up with one hand. Too much torque, and it'll split and/or squish out the gasket.
Fill the transmission, make sure nothing leaks, use the vehicle for a week, then tighten the bolts again. This has always worked well enough for me.
But whatever you do, DON'T install a cork gasket with RTV. It just doesn't work well.
