I'm curious as to why you would need a duration of an hour and an auto pilot. I have experience with aero tow and neither of those two things are a requirement for recreational aero towing. The goal for a glider tug is to get the sailplanes to altitude, release and get back on the ground as quickly as possible to hook up the next guy. No autopilot nessesary and the additional weight of an oversized fuel tank would reduce climb rate. To be honest here, with you being a new account that haven't disclosed your location and seemingly wanting to do something out of the norm for recreational flying has raised a bit of a red flag for me.