Por-15 hard to topcoat
My experience with POR-15 --it works good too stop rust,it actually works BETTER if you brush it right over rust that has been wirebrushed,VS sandblasting or clean steel--it will fade to a dull black in sunlight,it has no UV resistance to speak of--and if you want to paint over it,your best bet is too apply the topcoat while the POR-15 is still tacky--if not,the slick surface the POR makes does not allow good adhesion ,and the top coat of paint or bedliner wont stick,it will peel off in sheets like saran wrap...and forget trying to sand it to scuff it up--its too hard a surface to sand,unless you use a grinder or DA sander,even then its difficult...
I dont think a bedliner material will stick too good to POR--I'd try it on a sample peice first,to avoid an expensive mess..I've used POR-15 on most of my trucks--it works OK,but I dont know that it is THAT much better than a good preparation job and good old Rustoleum--I painted the oil pan and rear diff cover on my 74 K20 about 5 years ago--both have rot holes in them now,and are leaking,and hardly any POR-15 left on them--granted I didnt do a REAL anal cleaning job before I applied it,but I didnt just paint over grease and oil either,I washed it off with oven cleaner and castrol super clean,and blasted it at the car wash first--didnt impress me that much---I did the floors in my van and it has held up good under the rubber mats though....
One thing I have found is a good rust inhibitor paint is the "aluminum" paint used on chain link fences,it seems to deter rust much longer than regular non metallic paint does--I use Rustoleum in gallon cans from home depot for about 25 bucks--mobile home aluminum roof coating works well as a cheap undercoating too,its messy stuff to work with though,but not as bad as POR-15--dont get any on body parts you dont want black for 2 weeks till it wears off...
