Trucking PO's

Hello all. As we begin to use Flex more it would be nice to be able to monitor PO's for trucking from a subcontractor. This will mean we get even more detail in our Job Costing Tab.

As such what is the best way to achieve this? We have various Transportation Service options set up in Flex but we aren't sure if the best way to deal with this is to have the truck as a Sub-Hire or a Purchase PO.

Any insights from anyone already doing this greatly received!