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But it still doesn't answer my question! 
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Which one? Caulk? Foam board?
Have you laid a straight edge on that wheel to see if it is convex or concave overall?
Four holes for the lugs will lead to stress risers and failure. One hole can't eat away at itself. And if the wheel is convex, then a fairly large hole will center on the wheel.
Instead of caulk, wrap the edge with tape. Cut the circle by pinning the center and rotating the sheet material against a tool.