Interior Inverter EGC

[Land Shark]

Say, I'm installing a 1500 W DC-AC inverter as a sump pump battery backup in my basement and want to tie the chasis ground to a EGC. This particular inverter runs on AC and trickle charges the battery when power is available. When it loses AC power, it switches over to DC (battery) after a 4s delay. Any recommendations? The best idea I have thus far is to tie it to a nearby ground wire in an outlet box.

Thanks,

- Sharky