Josh,
I used some formed S.S. flanges that I had in my "spare airplane parts inventory", along with fire-sleeve & hose clamps. This is how many builders of other types do it. There are other ways to do it of course, and I think the grommets along with red silicone sealant is fine. You can see one in the first photo (BTW, the heater fittings in that picture are not the ones I ended up using). I ran all of the battery related wiring, as well as solenoid relay, charging system wiring, landing light wiring and oil pressure through the one on the right side of the firewall. Ran most of the other sensor wiring, tach signal, ignition, etc. through the left one.
Dave - I love your t-shirts!