I'm with the drive it 'til you can't any longer----at this point if its rusted and continuing to rust away it would be pretty crazy to start chasing those problems.
Adding in your mileage will necessitate an engine sometime soon you're fully into new-to-you van territory. If this van needed just an engine replacement that would be the easier and longer lived improvement. From your description chasing body rust is almost a no-win situation that becomes quite costly very quickly. BTW I'm in much the same boat with a work van---runs good (186K miles) but the body has issues I know can't be economically cured.
With the luxury of time on your side and assuming the budget permits I'd start looking for a suitable replacement. Depending on the range you'll travel for the perfect beginning vehicle there should be a few rust-free VGC vans to be had for a fair price close enough to inspect before purchase.
I'd search Craig's List via Search Tempest which allows for custom searches including distance from your home ZIP code. eBay is another great source with the benefit of seller's feedback ratings to help gauge credibility of an auction listing.
That's how I'd go about it anyway.............