Insulating the clamshells, a bad idea?
 

I've been seriously considering filling the clamshell rockers with 6lb. expandable closed-cell polyurethane foam for insulating the heat pipes and a little added rigidity (Don't quote me, but I read somewhere that it has a "R" value of 7 per inch and a compression of 200psi, it may cushion a side impact that hopefully NEVER happens). Now I've read several posts about keeping the drain holes clear on the clamshells, but how would moisture get in there besides through the drain holes? My clam shells are in excellent condition right now, and I've even coated the inside of them with POR-15 (I absolutely hate rust!), so what would be the downsides of doing something like this. All opinions respected and considered.

If I'm missing something obvious, please stop me before I do something stupid (it wouldn't be the first time!).

Oh, and a Happy New Year to all ya'll!!

I had to do some rust repair on my inner rockers. When I "was finished" I noticed that some of my welds were not the best on the bottom of the car (where the seam is). I didn't have time to finish the way I wanted to as I was in the process of moving. I good friend told me to try foaming the area as he had done so on an older IT car in a similar situation. I did so, trimmed and sanded any over flow then undercoated, primed and painted it (and fooled the concour judges in the street class two monthes later). The foam is still very hard (it's been 2 years), and being that it is closed cell, it repels water. I was told by my buddy that it is very suseptical (sp?) to uv light, but being under the car and covered that shouldn't be an issue. I do plan on fixing that weld this winter - I'll let you know if I uncover anything ugly.
On fiberglass the stuff is amaizing. I fixed a buddies 916 front bumper where he had crushed one of the forward extruding lower spoilers. We put the foam up behind (in side the cavity), then fiberglassed the outside - it came out great.
Scott S

Ummmm.....about redoing that weld. That foam wouldn't happen to be flammable, would it?

Well, it's said to be "Flame retardant", but if anything gets hot enough it'll burn. I shouldn't be having to reweld anything anytime soon as I really "overkilled" the corrosion control aspect of this rebuild. Plus it has the Brad Mayer (Sp) supports welded over the originals. But I could see where there would be a real mess if for some reason I did have to reweld something down there.

Thanks for the input!

P.S. -sccaracer-I noticed that you live down in Fenton, MO. I'm out in Pacific, by Six Flags!

Another hmmm... notice what happened where the factory foamed the rear fenders by the taillights and in the corner up above and forward of the the rear fender by the sail panel? From boat experience, I'd say that anywhere water can collect/condense needs free air movement to let it dry out. I think I'm gonna spray mine with oil each year till it drools out.
FWIW.

foam
 

a whole lot of detroit & japan iron is delivered thes days wirth LOTS of foam in the cavities; it strengthens the chassis a lot

BUT if you are worried about rust 35 yrs from now all bets are off