I bought a rear main seal from Autohausaz, which was supposed to come with a plastic crank "protector", but didn't. I assume it was both to protect the crank and facilitate seal installation by keeping the lip in place. I found an aluminum cat food can(Friskies) with the seal cut off and small slits up the side can be made to fit over the crank, helping(so I hope) to keep the lip in place as you tap the seal in place.
Edit: I guess Autohausaz didn't have the protector, that was from some other place I saw the seal, for about $9 more.