Thanks for the response.
The underside of the house is all sand and vented all the way around. I was thinking of sealing the underside of the plywood with a moisture and termite preventative I have seen sold at Ace Hardware before I secure it to the floor joists. Right now, I have the plywood just laying on the tops of the joists. I was thinking of nailing in some 1x2" pressure treated furring strips 2" down from the tops of the joists to lay the cut foam on, then seal any cracks or gaps with a compatible sealant or caulk from the top while it is open and easy to access. Then, screw down my plywood floor, possibly using a construction adhesive along the tops of the joists to make it even more secure.
For a little background on my project... I was going to "sister in" some additional joists to sure up the termite damaged ones, but decided it was just as easy to tear them out and start with all new PT beams. Essentially, I have a complete new foundation sitting on the piers.
Here in Florida.. the rodents have a field day with the batt insulation as was evident in the house where they totally dismantled my AC duct work for nesting purposes. Termites are no problem as I am experienced with them, their signs of intrusion, and a means of irradicating them... but prevention is half the job in fighting them.
Any further comments or advice is very much appreciated. I have some pictures of the project that will soon be posted on my web site. When they are up, I will add the link.