jroy,
I've recently been working on enclosuring a TF with 2x8's, on the inside we used a wind stopping textile, on the outside gyproc ( to create a shear diaphragm). This being in Sweden and here we don't have a SIP industry to speak of, this way was most economic ond gives good insulation values. As insulation we used cellulose that was injected under pressure through holes made in the textile. The cellulose was recycled newspapers from Englad! added with Bor, for fire safety reasons. On a trip in Vermont,USA, I saw a similar system but they had used recycled JEANS, and instead of textile they had used a plastic moisture barrier. The textile in our project was choosed to get a house not to airtight, with an airtight enclosure you need to keep a sharp eye on ventilation system. Of course, here we never install AC systems to keep cool during summer, so the problem with air tightness and ventilation might not be the same as for you. All I can say is I like the newspaper way and that it seems overkill (structurally) to build a 2x wall outsida a TF, but what to do: it's cheap and a nice system when it comes to installing wireing and windows.