Better yet, do use the 1/8" copper tubing as mentioned above, with compression fittings, use a long enuff piece of tubing and make a one or two double loop at the fire wall before going into interior to gauge and get enuff black 1/8 or 3/32 rubber vacumn hose to slip over the entire length of tubing to the grommet. The loop will absorbe vibration that could cause a break in copper and rubber hose will protect and color tubing black. Make sense? Works for me and I didn't stay at the Holiday Inn.
As for he rubber grommet issue, the Trifive chevy applications have such a grommet for wiper motor cable or you can go to Lowes and look thru their rubber or plastic blank plugs and fit as needed.