It looks like the udev rules are installed correctly. For me, it’s enough that 50-trezor.rules is put their as a symlink when rc.local runs. If you see those files in the disposable usb VM as it’s running when you try to use the trezor, I think it should work.
You say it can detect if the trezor is connected, but you’re seeing an error somewhere about missing udev rules? What do you do that produces an error? For me, when I plug the trezor in, I get a popup that says “Device available, Device, SatoshiLabs_TREZOR_… is available”, and then in a different app vm, I can run trezorctl btc get-address -n 1 and I get a prompt to enter my pin. Let me know where you’re getting stuck along the way.
One last thing I can think of is I have a trezor one. I’m very confident the rest of the steps of getting trezord and setting up the qubes-rpc stuff are the same, but maybe the udev rules are different? I doubt it but worth checking if all else fails.