To be clear, I believe you are looking to do the following.

AR-300M —> USB HUB —> (USB Modem + USB Flash Drive)

I don’t have a device to confirm but I would NOT expect this solution to work with the GL-AR300M-Lite version as it does not have GPIO Control.

The GL-AR300M16 has GPIO Control and my understanding is that GPIO Control will allow the configuration you are looking to deploy.

Again, I cannot confirm this but I can almost guarantee what you’re looking for will NOT work on the Lite version.