Hi Jim. I'm Jim Santos, IL's Roving Correspondent, and we have had to deal with this issue ourselves. You hate to pay for insurance when you are not using the car, but on the other hand, car rental prices in the US have increased greatly over the last two years. So a lot comes down to how long you will be gone on each trip, and where you can keep your vehicle.
We have found that if our car is garage-kept, being away for up to three months at a time isn't a problem. We complete any regular service required, and make sure the car is clean and the gas tank full before storing. I've read that reducing the tire pressure a bit helps, but we haven't tried that. We also once kept our car in a rented outside space (with an all-weather car cover) for 5 weeks while we were in Mexico and it started right up on our return.
Last April, we did sell our car, because we planned to be traveling for two or more years. However, a medical issue forced an early return, and we ended up having to buy a car again. In the future, we plan to keep our car, and like yourself, travel 8-9 months of the years in 2-3 month increments.
Hope that helps, and happy travels!