They do make a cargo liner for M550's with summer tires and a spare. Search on my posts. I posted a similar question but I ended up going WT because I could not find the one made by BMW for trunks with a spare. Someone did post a link to it after I pulled the trigger on WT.
Edit, found it and replied so it would go to the top. You should see it.
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2018 M550ix|Carbon Black|Dinan Modifications|2003 540i|Jet Black|M-Sport|2021 X5 Mineral White
Prior BMW's: 1987 325e|1993 740i|1998 740il|2001 530i|2002 745li|2007 750li|2006 750li|2001 530i|2012 535xi|
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