I installed a Eonon unit a couple week ago.

I cut out pretty much all the trim in that "hole" original HU sits, put the Eonon unit in, it sits pretty perfect.

It will come out with force to one corner, but otherwise, bumps and everything it won't fall.

If I need to secure it more, I would make some small tabs around the trim to hold it in.

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2002 X5 4.4
2007 335i - catless DP, Cp-e CP, CAI, MHD tuned ~17psi, AG m310 19's.