Need Help with Vinyl Roof Disease on '72 Scamp

I've said it before and I'll say it again. The problem with rust is that you usually don't see all of it. I bet that all the places Demonic mentioned are shot as well. Ask yourself this, where did the water go that all those huge holes by the rear window go? Into the trunk! So here is the deal, (I've said this before also), If you are a competent welder and you can fix all the damage yourself, then by all means go for it. If, however, you need to pay someone for this, sell it to cut your losses and start off with a nicer solid car.
Also, not quite sure what you meant by, "after I cleaned it up a bit, I realized it was a LOT worse than I thought when I bought the car". All the dirt in the world would not have covered up those rust holes. if you can't repair rust damage properly (welding in new metal) by yourself, then you REALLY need to start off with a much nicer car.