installing drivers on a bootable usb

Total novice with Linux.
Running Ubuntu 18.04 LTS on USB drive as tryout.
Computer= Minix running normally on Windows 10 pro.
Broadcom wifi drivers.
Ubuntu cannot see any wifi or offer a relevant download through software and updates.
I gather this is a common problem.
If I do manage to get the driver (somehow!) it will ask me to reboot.
If I reboot I lose the driver as persistence does not keep drivers.
So I can't do it?
Do I understand this correctly?
Thanks