Jayco X19H Roof does not support weight of solar cells?

Sounds CYA to me. If you have 1/2" Plywood laminated to foam, the screws should hold. If you have Wood trusses in some sections, that would be the ideal mounting point obviously. You're not risking warranty and I'm confident you will be fine in either situation as far as roof structure. If you don't have trusses to screw into and will just be going into the 1/2" plywood, buy some extra mounts and put 8 on each panel to add some additional strength instead of just 4 if that makes you feel better.