409, garbage bag and a steamer. Spray the film with 409 liberally, bag it and park it under the sun. This works on its own more often than not. If the film is very brittle and keeps breaking, pull out the steamer and slowly help it along with the additional heat.
Sometimes you only have to bag it for 15 minutes, sometimes an hour. If the film pulls off but leaves a ton of glue, respray and bag it again until the adhesive turns to snot, then 0000 steel wool it.
If its overcast/winter, you will need a few heat lamps on stands to warm the entire back glass up, just be careful how close you put the lamps for obvious reasons.