I've done this and it is very straight-forward.
I just duplicated (insert and stay) the oob one for incident, but changed the table to interaction. I then adjusted the script on the action tab appropriately (for field names on the interaction table instead of the incident table). I also created a new one (copied from "forwarded") so that replies to emails create new interactions. We do this because if one of our agents replies to an email, they do not know if there will be any follow-up email from the customer and we do not want to have a lot of open interactions that need to be closed periodically if there is no reply...so we just always close the interaction after replying to the email and let it create a new one if the customer emails us back again.
