What exactly is the big whoop about leather seats? Someone please explain????

As for water-proofing leather..... only way to do it is to let some viscous water repellant material completely saturate the whole thing. Pressure treated lumber process does this with wood preservatives, i'm sure a process for leather could be fashioned, but it would likely not be DIY. Short of that you could use a mix of casein & bee wax.

- Andy