Prep work for applying POR

[1970blazin]

#1What do I need to do to prep the interior of my blazer to apply POR?
#2 What is the diff between POR-15 and POR-30??
#3 Is this the best way to keep my blazer interior rust free for a LONG time??

I am planning on wirewheel & grinding the rest of the bed to get it clean (I already sandblasted a few areas, and the floorboards and kick panels are all new metal) Then after applying the POR I will probably use some kind of sound deadner (Like dynamat, or Brown Bread) Any advice appreciated!!