It can probably work while the system is on but there is virtually no way it can hold any backflow if your pump dies/power goes out.
If your system back drains 2" from the display is off, that's approximately 15g of water back flow (most likely more). Your sumps est max capacity is ~26g when empty (there will definitely be water/other stuff in there so it will be less)
I highly recommend you buy a much bigger sump/tank/tub to use if possible for peace of mind (in the event of a pump failure/power outage) + gives you the option to use bigger+better equipment.
I usually pick my sump size based on the maximum possible back flow gallons if the system were off + sump operating water.
For example with your planned 180g if we have 5" of backflow then whatever sump you get needs to be able to hold 38 gallons of water in addition to whatever water would normally be in there.