Progress is slow. I'm +12 hours on the chill test and am only barely under 70*F. Thinking it was a case of insufficient heat transfer through the vinyl tubing, I checked the temp on the reservoir of coolant. It was only about a degree cooler! To me, this indicates that the heat transfer through the vinyl wall from the corny to the transfer liquid is not the limiting factor, rather it is a slow process to cool the 5 gallons in the corny + the volume of the coolant. The coolant bottle in the keezer is only about a half gallon or so and with the small pump running continuously, I don't think it dwells in the cold long enough. I may need to slow the pump and/or increase the reservoir size. If my theory is right, it should continue to drop in temp, albeit slowly. Since I'm always above freezing, I've just been using iodophor/water. I'm not sufficiently thermodynamically knowledgeable to know if using an antifreeze type product would more efficiently heat/cool or not.
Before anyone asks, the reasons for using vinyl were cost and easy of application. That much copper would be $$ and a pita to roll, add fittings and attach to tank in keezer.