Leak-free Class-C?

The cabover will leak due to the inherant flaw in design. The ceiling rafters, as they are run the wrong way. The front window floats in its 2x2 frame anf the roof seam generally runs at the curve of the cap . If one were to video this unit going down the road you would see the cab roll and flex in the wind. Any seal will work loose in time. I corrected my problem by removing the ceiling and building laminated plywood struts, like the wings of an airplane, supporting the curve of the roof and tying the front window to the framing. All seams are taped with eternabond and painted with flex seal type paint. Inspect and reseal every year. I didn't last year. I have a leak now at the gutter rail into one of my cupboards. I'll need to wait until spring to fix it.