Paint prep, body repair, and beyond

[tsroark]

So, just registered and might as well jump into the questions.  I will be replacing the front clip and cab of my truck very soon.  I do have an entire front clip sitting in my driveway now, and that's one of my hang ups.

The fenders do have very minor surface rust so i want to strip them to bare metal and kill rust before it becomes a problem.  I was going to just sand and wire wheel them down but then I thought of the insides.  The insides could very easily fill with water/crud and sit rusting away and I would be none the wiser.  What can I do about that.  could I just poke around with a mirror to see if everything's ok then fill them with expanding foam?  Or do I have to have them done professionally?

From what I have found, the right bed liner can make good undercoating/rustproofing.  Am I right in this assumption?  I am planning on doing the underside of the cab, floorboard, rockerpanels, wheel wells, and a stripe around the bottom of the body and maybe around the fenders.  Mostly on some of the rust prone areas, just to be safe.  And can bed liner be sprayed/rolled/brushed on top of paint or should I do primer -> liner -> paint?

[thirsty]

I would not put expanding foam in those areas. The foam will hold moisture in the parts eventually in my opinion. On my daily drivers I use Fluid Film to keep the salt at bay during the winter.

http://www.fluid-film.com/index.html

I would do any body work and paint before using a product like fluid film though.

[tsroark]

Thanks for that, the expansion foam was kind of an iffy idea to begin with.  But the big question is how do I strip and repaint inside the fenders?  Or will they have to be redone professionally?  Or should I even worry about it if I cant find any evidence of rot?