Chevk and see if you can put the fan behind louvers that open when the gable fan comes on.
Roof stores and home centers has louvers. I checked recently and Loews had better louvers than Home Depot. Each louver has a strip of rubber on the bottom that minimizes the clanging and probably helps it seal better.
Also, you can get fans with different CFM or air-moving power. Use a thermostat and a humidistat (for winter venting of moisture). --Billy