Long answer short....nope, I have not dealt with the problem
Longer version: Coleman and/or Fleetwood are likely taking the position that their sole obligation is to serve the original owner because that is the only party to whom they have pledged any sort of promise of suitability for any purpose. Any subsequent purchaser would (according to them) have to seek non-warranty service from the party that sold the vehicle to them.
As for remedies, I wouldn't hold lots of hope for the rubberized roof coating whether it is rolled on or an actual rubber membrane. The problem is that the molded roof pulls things together structurally and maintains "square". Putting a rubber coating or cover on might stop rain penetration but it will not renew the structural rigidity. The crack, once formed, is affected by heating and cooling and the forces on it from movement which make the crack larger which etc, etc, etc. Cracks in automobile windshields or airplane canopies suffer similar problems.
You might be able to stop-drill the crack. Take a small drill bit (just slightly larger than the crack but not not "big" and drill at each end of the crack - make sure it is a sharp drill because you want a clean hole. That may distribute the stress and allow the crack to stop it's movement/growth. Then, use the rubber treatment.
If you get real ambitious, take the roof off and peel off the skin and make a form for a replacement then create your own with fiberglass cloth and resin. It is messy but you might be surprised at how quick you pick it up.
Or, you could call it a life lesson. Sell the camper to someone who wants it for hunting 'n fishing trips and can deal with minor cracks to be off the ground and out of the majority of weather and buy yourself another.
I would never suggest you do anything, ummm, unfair. But, do you still know the original owner? Know him/her well enough to let them take "their" camper in for replacement?[:(]