Best practice for earth connections on isolated equipment
I'd advise you to ship with a US style GFCI (Ground fault circuit interrupter). 



Above picture from here.

This is because any building GFCI will not be able to detect potentially dangerous live leakage currents to earth that occur on the isolated side of the isolation transformer.

So, you would wire as follows: -


Normal mains from board to
Isolation transformer input
Isolation transformer output to
GFCI then
GFCI to equipment


The "equipment's" earth wire should connect to the earth from the main switch/fuse board (the same as normal equipment directly connected to the mains AC).