Body work that will last!?

[tungsten]

Hey guys, Have a few questions about some problem spots on Mustangs...

Seems like every 65-66 Mustang I see has a crack at the rear of the drip rail where the quarterpanel meets the roof. What is the right way to go about fixing this so it won't pop up again through my new paint job?
http://memimage.cardomain.net/member_images/5/web/113000-113999/113040_98_full.jpg

I also wanted to add some body filler to the seams in these pictures, whats the right way to go about eliminating the seams?
http://memimage.cardomain.net/member_images/5/web/113000-113999/113040_99_full.jpg
http://memimage.cardomain.net/member_images/5/web/113000-113999/113040_96_full.jpg

[silentdub]

To hide the seams, on my 67 Camaro, I grinded, welded it up, grinded, then filler. I welded because if it were to flex a little, then it would crap the filler.