Most of the Jayco warranty is their passing along whatever the component mfg's will cover, supplemented by their own coverage. So, I doubt strongly that as long as a modification you made did not contribute to the cause of the warranty claim, they would make an issue of it. If you blow out your AC, that will probably be on you. But if your roof leaks, or a slide stops working, then Jayco shouldn't have an issue.
From the Whitehawk manual: "Jayco’s limited warranty only covers substantial defects in materials, components, or parts of the RV attributable to Jayco". Nowhere does it say that you can't make modifications.
2012 Ford F-150 Eco, Max/Max
Jayco 26.5 RLS, Reese Sidewinder