Either width is okay on a big road which itself has no problems. But 96" is
much easier to live with, intuitively, on two-laners with no shoulders, turns in small towns, fuel stops, and many rv parks/campsites, IMO. This is true even with 20' construction trailers I've noticed with others towing: crossing over into another lane w/o quite being aware of
just how far over. Granted this tendency is reduced with a 5'er/GN hitch arrangement.
You've set yourself an impressive set of design goals.
Will you're be going with onboard air (such as
KILBY or
VMAC) for fairly fast, high-powered suspension-height changes. Air tanks near the trailer front?
Sure am looking forward to this. Will the present Avion be the "donor vehicle"?
.