It sounds like enabling Mesh will be a good solution for hard-to-reach location. Just make sure you have good signal strength from a wired AP in this area.
Can you clarify that you have both ZDs on the same VLAN? In my experience this would normally cause problems as the ZDs would conflict by trying to adopt each other's APs, as ZoneDirector has L2 discovery and adoption.
Please be aware that once SmartMesh is enabled on a ZD, it's not possible to disable it without doing a factory default, so ensure you take a config backup prior to enabling it. However it is possible to disable Mesh on an individual AP basis.