The PVC i am using is 1/4" thick so its not brittle by any means.
Also, PVC is heat resistant therefore even if it does sit over the engine it doesnt affect it. Besides, the valve cover doesnt give off much heat..and our stock air box goes over the valve cover, or engine if you will, same way that mine does.
Just as a side note: The most reputable cold air intakes in the Ford community and some others (cant recall) use PVC specifically to gain a cooler charge over competing brands. Check out JLT Cold Air Intakes. they have LOTS of research done proving so.
Lastly, i really dont see the filter being in a dead air zone at all. After driving an hour, and i open the hood the filter is cool to touch as the hood on the TJ doesnt have any weather striping around it therefore air is constantly flowing in, in between the hood and fender. I had the filter seated where the stock air box was for a week and after driving in snow it was all white from the salt and water seeping through the gaps by the lights and the grill. Mounted where it is now, it is still very cool to touch and away from the header and all other engine heat.
Test it out. Just leave a filter on top of the battery for an hour and take a drive with it. (dont actually install it, just place it on the battery and secure it there somehow and after some driving when the temps are up, open the hood and see if its hot. I bet you'll be surprised to see the results....
And i am not comfortable leaving the filter out in the open because of the rain, excessive debris and such just to gain 1-2 hp. Not worth it IMO, although yes it would
certainly be better and more effective.