I'd suspect that the lack of pliability of your rubber diaphragm is due to the fuel evaporating from the bowl after the truck sits too long. I think if the rubber stays wet, it's less likely to dry out and become stiff or cracked.

I drive my truck hundreds of miles each week/month which might be why I have had no problems with the diaphragm failing.

I'd suggest driving your car every few days or at least turning the engine over to keep the fuel bowl full and the accelerator pump submerged in fuel.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)