So.. to "seal off" the inlet at the fogger.. well, you really can't do that... the fogger needs a couple inches from the inlet so that the air right outside the nozzle mixes with the juice to form the fog. If you were to cover that up, I would imagine the fog output would be a lot less.. I don't know for sure tho. That said, one way to do this is to use an angled T joint as the inlet. It looks like a Y shaped PVC piece. You fire into the inlet that goes straight, with the other end of the Y near the nozzle. This is like a back flow thing or something. I forget the science behind it, but apparently it does two things.. and I think the main reason for using this is so you can do what you are suggesting.. if you put the Y join right up around the nozzle so that there is no gap between the fogger and the inlet of the Y joint, the extra leg that forms the Y allows air to be "sucked in" as the fogger sprays, so it in effect provides the air the fogger needs to product the fog. Someone with more knowledge may answer better, but I think this is why it was used, to avoid fog seeping out around the inlet.
I too would suggest using the PVC or ABS for it's smoothness and try to avoid too many elbows. It is definitely going to be harder to do a 12 degree rounded edge with it tho. With dry ice packed in it, 3" should be plenty in diameter.
I know 45 mins is a long drive, and for a slight bit of fogging it may not make much sense. If you had a big fog machine, or a couple of them, I'd recommend it. If not, perhaps you can put a ton of ice in a chest, add sea salt or whatever to help lower the temp a little bit, then stuff all that in your tubes.
If I get my 960 before halloween, I will probably end up using the PVC with dry ice chilling method this year. I built 2 fog chillers the past two years, and ended up forgetting about them when we moved and they were trashed!! So I don't know if I am up to building another one.. at $30 for the 60qt igloo, and another $15 or so in parts.. while it would be worth it, the 960 is going to be WAY too powerful for that chiller. I am hoping I can turn the output down to about 30% or so so I can get a somewhat continuous flow without the reheat cycle!