I have to replace my distributor nearly every year

Every winter when the weather gets moist and damp the vehicle has trouble starting. When I replace the distributor cap it fires up just fine. But this is getting ridiculous, every year? When I first bought it in 2007 I replaced plugs with non AC-Delco and the check engine light came on. Codes say "random misfire". Car runs fine with new cap but CE light stays on all the time. Could slightly bad timing be hard on the caps?