Database design for a reservation system with assets which can travel between locations

Database design for a reservation system with assets which can travel
between locations

I'm developing a database structure which consists of assets which travel
between a couple of locations. I want to make a reservation system for
these assets. If assets don't travel between the different locations it's
very easy to get the availability: just check how many reservations for a
certain day exists and substract them from the normally available number
assets.
available = Normal.Available - already reserved
But the complicating factor is the fact people can travel between
different locations. A customer can pick up an asset at Location A and
drop it of at Location B. For instance pickup on september 13th 10:00am
dropoff at LocB september 13th 13:00.
If I now want to have the available assets at Location B at 13:00 this is
the normal available number +1 because of the asset which travelled from
A->B. The availability at location A is one less then normal, obviously.
How can I graph these movements in a database structure?