So there i was, pondering the front hatch seal......again. And then it came to me.
So i got an inner tube from my racing bike, partially inflated, the excess, folded up at one end, bind with electrical tape (sorry about the photo)
Form it around the hatch
The hatch cover bungees provide nice even pressure across the whole seal, and the seal, being filled with air, naturally forms around any irregularities, deformations, and will self compensate for any flexing of the hull. Some sticky velcro to keep it in place.