For quick and easy, try this download link where I've applied all the filename extensions for you:

http://gurce.net/c64mini_files/doom_MVADB0B1B2B3B5.d64

If you'd rather learn the configuration steps involved to roll your own:

• Download the .d64 file from Kweepa's github repository at:
  • https://github.com/Kweepa/vicdoom/raw/master/doom.d64
• Rename the file:
  • From: doom.d64
  • To: doom_MVADB0B1B2B3B5.d64
    • MV = This sets the computer model to be a VIC20
    • AD = Accurate disk emulation
    • B0/B1/B2/B3/B5 = Turn on all the banks of memory expansion
• Drop it on your usb stick
• Fire it up on your THEC64 full-sized and off you go! :)