Has anyone used Nitrogen to fill their dinghy, like you would use in your cars tires? In an effort to offset the loss of air in temperature swings, and the softening of dinghies that happens. Is there an adaptor available for the conventional air valve to do this?
First, all gases even water vapor, expand and contract with temperature the same there is no advantage to any, per Charles' Law.
That said, Nitrogen is used in race tires because, although a smaller molecule than oxygen, it is significantly less permeable to rubber than oxygen, and therefore will "lose" less air per race.
In normal passenger automotive tires nitrogen being inert does not react like oxygen with rubber, producing less cracking in the inner liner of the tire, and thus less loss of "air' with aging.
Nitrogen in a dingy however is probably another story, as with a tire, temperature effects will be the same as "air filled", loss due to permeability will be different as Hypolon, PVC, and Neoprene are all better than rubber having less gas permeability.
Over all not worth the effort is MHO.