LonisOvril 70 - 75 C (160 - 170 F) is enough to keep filament dry during printing, but I have found it to be too cool to dry already wet filament no matter how long it is dried for. This applies to Nylons and PET's.
185 F (85 C) is what I dry at with very good results. Unfortunately this is a bit hotter then commercial driers get (not sure why either, as it's both safe and easy to get a little hotter). I modified a Magic Mills drier by wiring the heater to always be on, and it runs at 185 F. You could do the same, or maybe use a toaster oven, assuming the oven has a convection fan to keep the inside temp even. You may have to do some hacking to get the oven cool enough.
Final point about some filaments being too far gone, I have observed this with Nylons that were left out for several years. Even with extensive drying they still have stringing and other water related issues. I don't know the cause of this on reversibility, but it only appears to be an issue after the Nylon was exposed to high humidity for a long time.
