i used the thread that was posted while back in this section concerning dash repair.
i first cut off the extra material that made the cracks not flush with the rest of the dash. I then used a type of hardening expanding foam to fill in the gaps. I believe the the product i used for that was called "hulk" which i got at home depot. Once the foam expanded and dried i shaved the excess and prepped for some flexible bumper repair. its made from Bondo, heat resistant and flexible.
here is the picture of what it looked like. kinda expensive but it was the only stuff that was around here in Santa Barbara, used about two kit for my whole repair.
From that point i let the repair kit dry and started sanding. After a few hours of sanding, got it to the point where it was nice and smooth. I prepped for some wrinkle finish from Krylon and let dry for 24 hours.
next day i prepped it for an adhesion promoter that came in a can, let it sit for about 20min and sprayed my last coat of Vinyl and Fabric paint... Duplicolor worked really well on the dash.
If you were to use bondo (auto body bondo) i think it would crack do to the heat within the compartment of the car. You want a material to go over the dash that is flexible under heat conditions to prevent craking of the dash. Auto Body Bondo would keep its place but the rest of the dash would pull away and create a new crack. Thats why i went with a bumber repait kit, its flexible under any condition and will stay in place.
hope that helps
oh yeah total cost was about 45 bucks, a dash repair is worth doing!!!