Armor All is fine and doesn't dry out vinyl but, like almost all
protectants, instead prevents that from happening.  Some people say 303
and similar products are better since they apply plasticizer to the
vinyl, but I don't know if that's actually an advantage.   It helps
greatly to keep the car shaded (even a very light cover is beneficial)
and put a fuzzy polyester cover over the dashboard (it lasts forever,
unlike velvet, which turns to powder and its foam underliner crumbles).
Even better is to line the bottom of the cover with white material,
such as Tyvek or even cotton that's been washed in laundry detergent
(the brighteners in it keep out 98% of the sunlight, compared to about
80-85% for untreated cloth).

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You need a specialized vinyl product, not saddle soap.

See:

http://www.303products.com/main.php?infopage=protectant