Tips for drying:
Convection in the oven is a wonderful thing! It helps create an airflow around the oranges for drying. However, if you don't have it, don't fret. Cracking the door open and using the wire rack also assist really well with drying. You may just need to leave them in a little longer.
You may also dry at a lower temperature (down to about 130 degrees) if you desire. Once again, you just want to continue to check the oranges about every 30 minutes, rotating them to avoid hot spots that could end up burning. Depending on how low you go, it could take considerably longer, but low temperature is key to not burning and having perfect chewy results.