So Glen Coe is your final stop, but is Fort William also your first stop? If you’re renting there (and do you already have your rental arranged?), and presumably driving a loop, returning to Fort William at the end, that could be efficient. And if driving thru Glen Coe is a definite finale to your trip, then you couldn’t simply pull into Glasgow and return it there, before proceeding g to Glen Coe.
Or, if you’re renting in Fort William, could you head a bit east, and have Glen Coe at the beginning, before doing the rest of the trip? Or start in Fort William, get your car, drive your trip, with Glen Coe the penultimate destination, and then drive on to (or near) Glasgow, where you could turn in the car, and wrap up the trip its final night?
For what it’s worth, our trip back in 2013, Glen Coe was in the middle of our itinerary - towards the end, but not the final destination. We picked it up in Inverness, and returned it at the Edinburgh airport - no charge for the separate locations. We had it for a couple weeks, including Fort William for 2 nights near the end. Leaving Fort William the next-to-last day, it poured rain just as we got into Glen Coe, so we stayed in the car, windshield wipers going at full speed. When the storms ended about lunchtime, we pulled into a pub to dry out, have lunch, then continue east, to Doune and Sterling. Spent that last night in a B&B a fairly short drive from the Edinburgh airport, where we turned in the car and flew home. No train involved.