I use butyl tape. Comes in a roll and is super sticky and doesn't make a mess when you need to remove the panel again - and it can be reused! I get mine at an RV parts store, but if you did an internet search for "butyl tape" you will find all kinds of options.

Good luck!

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1995 E300D - 193K and $28K in maintenance!
1964 220Sb - 318K, second owner
1997 Passat TDI - 190K and 47mpg