Are there any parking garages anywhere? How about parking at the airport?

Where would be a good place to park overnight in Flagstaff?

We're planning our first overnight bikepacking trip in a loop around Flagstaff and I was wondering where we could park the truck without a lot of worry about getting towed or broken in to for the 30 hours or so we'd be away.

I initially thought about the Walmart at I-40 and I-17, but I don't know if they would allow it.

Any ideas would be greatly appreciated.

Thanks