Jason,
The RTV works great as long as the surfaces are clean, and you can let the rtv sit for a bit before it is reinstalled. then let it cure for a while if you can before refilling the diff. I let mine sit over night- I do have a few other vehiocles avail so that may not be an answer for everyone.
I use lacquer thinner to clean the surfaces of the cover and the axle. Brake cleaner , mineral spirits, or some other low residue solvents work well also.
Have fun, oh yea I wear disposable rubber gloves when working with diff fluid- the smell is hard to get off your hands (or clothes,tools, garage floor etc) , something to think about. You can get a hundred pairs or so for about $7 I think.