What is the lowest and slowest way I can bake pork ribs?
To achieve "done" pork ribs should reach an internal temp of 160°F (71ºC). The longer it takes to get there be more tender they will be. I would not recommend going any lower than 200°F (93ºC) for your cooking temp, even if that means turning the heat up a little at the end to reach your internal temp of 160°F. Put a good rub on, wrap the racks of ribs (individually) in aluminum foil, with some beer or cola in there (or other braising liquid) and let them go. For a video of how to do this watch this episode of "Good Eats" All of that said, I have never tried to let the ribs go 7 hours unattended, so I would try it when you have the time to hang around and monitor the internal temp, again looking for 160°F internal temp and that will give you a means to determine what is "done".