Hi Steve, This will probably get moved to paint and body.
I've done my whole chassis in POR-15 ,but as yet it hasn't seen the light of day!
I wasn't planning on top coat and as you have already mentioned it won't get direct sunlight.(If we ever actually get some here!)
I don't think the protection degrades I just think it's a cosmetic issue.Another option would be to top coat the areas that might be directly exposed although I can't think which parts this would be.Once all the panels etc are on it should be all covered.
I'm sure someone else will chime in who has used this and will give you more advice.
Jock thumbs_up

Last edited by jockbolter50; 03/10/2009 9:10 AM.
1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.