I think you'll find that just for plugging a hole in sheet metal a simple plastic or rubber plug will seal better than a Chrysler christmas-tree plug or a metal plug with fingers.
The Chrysler plug is used on trim panels & to hold wire clips, etc. on the the sheetmetal, & its 1st stop is a little farther in than the thickness of the sheet metal on the body. It may be a little looser than desired & could admit moisture. I'm-a lookin' at one now that I replaced in the Neon.
A metal plug with clips will definitely not seal as well as a plastic-faced one.
At Lowe's hardware, they've got half an aisle of weird fastener doodads, grommets, mirror clips, etc. They've also got plastic plugs for various diameter holes that have a narrow depth before the rear flange that is appropriate for holes in sheet metal. There is one now in my GT6 filling the hole for the antenna, that I put there after rescuing my car from Satan's body shop, where they pulled off a lot of things including the antenna then parked it outside for weeks to let the rain get in it. I haven't missed the radio, but I need to put the antenna back on for appearance issues.
Anyway, Loew's has got a good, flat, black plastic plug made for the job that you'll like.
I'm pretty sure the nutria will be able to wiggle that metal one out, anyway.