I'm looking at some class b vans, no slides, no roof, no cracking overhead caps.
I will always support going slide-less if you can live with less elbow room, and your floor plan can accommodate it.
rvrunner, This won't help address your situation, rather provide a possible cause, why the crack may have developed.
I got this picture from Phoeinx's construction slide show. The shell of the van is structurally compromised from cutting the roof to create a friendly pass-thru between cab and cabin. Almost "every" RV manufacture does this with their B+ and C class motorhomes. Not only is structural integrity compromised, encouraging such stress cracks, but "side impact" and "roll-over" protection is also compromised. Add in 122,000 miles of an overly stiff suspension and rough roads, though very rare, bad things can develop like rvrunner is dealing with.

So what can we do to prevent this from happening to our PC's? Soften the ride to reduce metal fatigue.
1) Weigh your rig, then adjust your tire pressure to that weight. Over-inflating your tires will make for an unnecessary rough ride.
2) Make notable effort at softening the ride through spring adjustments, most especially to owners of PC models 2100, 2350, and 2400, built on the E450 chassis. Consider what I did
HERE with my front suspension. Also consider doing something similar with your rear springs, removing one or more leafs to lower your load margin to soften your ride. You want roughly 500 pounds of extra load margin between what you actually carry, and the GAWR of each axle. Your house, your contents, and you, will all appreciate a softer riding PC.