Trucking/Vehicle Availability

I'm wondering how other people handle the availability of trucks and other vehicles.

Right now, our trucking is setup as a Service with different price tiers for different distances. The issue we have is there's no way for Flex to know how many of each vehicle we have and when we have conflicts/shortages.

I've seen in other posts that some have added their vehicles as Inventory items so that they can track availability the same as any other piece of equipment. How are people implementing this?

Our vehicles are only in use for drop-offs and pick-ups, so they are available during the time in between. Do you add different Subtotals for drop-offs and pick-ups and then adjust the Subtotal time to reflect when the truck is in use?

This would apply to box trucks hauling equipment, as well as company vehicles used for crew transport.