Sean wrote:
Does anyone know much about PTT ?

If you dig a hole, put in some hardcore/gravel and plonk in a PTT ... back
filling with more gravel and compacting ... how will it fair with the
elements?

Basically, is it really necessary to concrete the posts in as they will be
securely held in place by the (above ground structure).

32+ years ago I built a dog run in the yard. I did it on the cheap and
used regular 4x4's that I dipped in Creosote and then coated (the bottom
30" or so with roofing compound). I dug post holes, put a couple
inches (scant) of septic stone (smooth 3/4" to 1¼") sunk them in and
backfilled with dirt. About 10 years later we pulled them out and found
them soggy but still sound enough to keep the fencing taut.

Put in a swimming pool deck around 1988 using PTL and again, with the
4x4's otherwise untreated. This time the holes went down 32" and a
good-sized dollop on Sakrete went in each hole forming a "cookie" at the
bottom. Posts went in as they came from the lumber yard and back-filled
with dirt and a bit of water to settle things in. Got rid of the pool
circa 2002 and the new owner took the decking apart, including the
support posts and rebuilt same on his site. They were as solid as the
day they went in.

My experiences, your mileage may vary.