I also had a roundy van body from hell. Admittedly mine didn't have any rust in the seams.
Bottom side of the floor.
Inside you can see the holes where the floor meets the cross memeber:
It's taken a fair bit of work but all the cancer is gone.
But I totally underestimated the amount of rust that was in the car. In the beginning I could see the rust holes in places, but once you start removing bog and tar and finding more, you can feel overwhelmed.
Go see my blog for more photos and details.
If you enjoy welding, and have the time, I'd say do it.
Otherwise, I'd say buy a less rusty clubby van and put a roundy front on it.
I have been looking for a replacement shell all while doing the work. Nothing decent has came up close enough in the last year. Now I think I'm too the point where it is not that hard to finish. So yeah, I'd agree that finding and good roundy van shell is hard (up here atleast).