As far as I know handling is no longer mandatory if you park on the south side (GA side). The only problem this seems to present to people is getting transport. Speaking not from experience but from others' tales, if you want a taxi to the main terminal they are reluctant to come round to the south side for the small fare, but if you are going into Douglas etc. it shouldn't be a problem. I believe if you ring the tower upon return they will send someone to let you back through the gate. Landing fees last I know are invoiced by post.
You do also have Andreas in the north of the island. I have never been there. It is more out of the way if you want to go to Douglas and I have heard that the surface conditions are bad.