I would try to get away with just using Zyrtec ( = cetirizine = Reactine ) 10 mg daily for a dog 15-39 pounds. It's an antihistamine with almost no side effects. All the other drugs mentioned have quite severe side effects with long term use:
Atopica= cyclosporin, also used for transplant patients to prevent rejection,causes major suppression of immune system
Temaril P= phenothiazine antihistamine ( sedating ) plus prednisolone- the prednisolone suppresses immune system plus can cause cataracts, diabetes, osteoporosis etc
Apoquel= JAK inhibitor, biologic therapy- long term follow up study over a year showed 6.7% rate of serious side effects according to monograph, 4% were cancer, 2.7% other serious illnesses.