Basenjis need to be trim and elegant for their own health. An over-weight dog is not always a healthy dog, weight puts unnecessary strain on the organs of dogs, just like it does on humans.
27 lbs sounds overweight to me. Even a large framed dog shouldn't go much over 25. Feeding him twice a day, balanced meals, identical night and morning, will help you control his weight.
If you weigh out his kibble ration each morning and give him bits of that - if you must five him treats- then the treats are coming from his daily ration and are not 'extras'.
At his age, try and take a pound off and keep him slimmer rather than plump. You are supposed to be able to fit another half Basenji into the same skin. The ribs shouldn't be well covered !