Two questions:

1. Some SIP munfucturers use mastic and some use foam. Does any have experence with both and have an educated opinion? I'm guessing the mastic, because it is non-hardening may perform better long term, though foam seals larger cracks. Has anyone done blower door tests on house having both?

2. I notice the Preimer mastic was in a base of naptha! Not exactly low VOC. Anyone have a low VOC option that works well?

Each has its place. For a tight fit around bottom plates, panel mastic works well when properly applied (no gaps in the applied bead)

The foaming option works better where joints are wider. for instance a roof panel joint that is open up to a 1/2" can easily be completly sealed by injecting an expanding foam.

Beware of the limitations of both single component and two-component foams. Each has its pros and cons.

I teach the combination of using both mastics and expanding foam to properly seal a panel structure. In addition, we use rolled sill seal, adhesive backed foam seal and a variety a SIP tapes. The proper method is a fuction of the type of joint and what type of climate you're building in.

As for panel mastic and VOC's, the two main manufacturers that make the stuff are OSI and Sovereign Chemical and they both contain VOCs. Some panel providers will spec compatable caulks and a few of those are either low or no VOCs.