The Insulator is the 'resident expert' on this one. If he doesn't come along soon, he leaves his e-mail address on his Follow-ups. I'm sure he wouldn't mind a direct contact. BE sure to let him know the title of your particular Post so he can respond to it on-line for all our benefit.
In the meantime, our home didn't have soffit vents either. It had gable vents too and a ridge vent. (We've since put in soffit vents and the attic is a lot happier.) We didn't finish off the attic into a living space. We wanted to keep it unfinished and use it for storage like you. Even with 'proper' and 'adequate' ventilation up there, don't store anything that will get damaged due to extreme heat and cold. Photos, paperwork, fluids, and the like will get damaged or cause damage down the road. I don't think anyone would consider an attic as a 'cool, dry place' which is something you read on almost EVERY label when something is storable.
The previous homeowners did install a fan at one gable end. It didn't work well at all since the ridge vent 'intruded' on the flow from the other gable. I'm sure if the ridge vent wasn't there, there'd be a more direct ventilation THROUGH the entire attic. If you end up putting a fan in the gable or on the roof has to blow OUTWARDS. Otherwise, you'll bring in snow and rain and such into your attic. That would be bad.
As for ice damning, forget about those heating strips you install on the eaves. Venting is your answer on this one, I'm sure. Once you get proper venting, there's not need to insulate the rafters. There's more to this aspect of the job than you think. (You'll need soffit chutes.)
By equalizing the attic temperature with the outside temperature is what you want to do. When the temps differ enough, THAT'S when you get problems like ice damning.
The Insulator will most likely chew my Follow-up a bit but keep the common-sensacle parts in mind. My best to ya and hope this helps.