i was very lucky with my chally. it had a vynil top, and it was already removed when i got it.
the roof was exposed for several years, but after a good thrashing with 40 grit, it came out ok. i only had to repair one spot on the passenger side. after sanding the wee out of the roof, we covered it in ospho.
makes it turn black and nuetralises the affected areas.
i agree, the best way to see whats up, is find out whats under.
be prepared for the worst, and you may not be that dissapointed.
best of luck.