Lowering the Battery - Grommet advice

[Redjay]

I'm lowering my battery to the lower rear cross member as part of my turbo build...

https://midshiprunabout.org/mk3/moving-stock-battery-to-rear-lower-cross-member/

The chap in the link drills into the crossmember, so the battery j bolt can be attached, and advises putting some rustoleum on the hole.

Im thinking a decent rubber grommet might be advisable. Does anyone have any idea what type of rubber grommet would be up to the job? (cheese is not an acceptable answer).