Well, this is a future project for me. I have a 3rd gen with the din and a half stock radio. I am looking at doing a double din DVD player later when I win the lottery. I spoke with the dealer and they can supply a new double din dash benzel (around $200). But while writing this post this is what I found, very interesting!!
Anyone do Double DIN in Dodge Ram yet?
Not sure what year your truck is, but for a 2007 $200 is about three times too much. Check eBay - there are `06-`07 bezels on there for around $70 most times. Should be true for other years as well.
ETA: - Apparently `05 and earlier trucks only have 1. 5 DIN. Gotta cut and mod for a double DIN unit.