I didn't find any good options for mounting my camera to a metal structure in the garden, so I made one. Works well as long as it doesn't get too hot for your filament. I mounted one of these on a gutter and the PLA folded up due to getting soft and CTE difference between plastic and metal. When mounted on a bulkier high mass surface it has worked great.

Link for the magnets that I used below. You'll need to to glue them in with superglue, and you'll need 10x of them.

Original model link shared below in case you need to modify.

Model:
https://cad.onshape.com/documents/9486cd4e1a6844dff7f0ee7f/w/68d91dcf481ba0287cbbb857/e/aad245a03898f7abda5e488d?renderMode=0&uiState=684db7b78ef40d5da3cb9220
 

Magnets (Qty 10)
https://www.apexmagnets.com/magnets/1-2-x-1-8-disc-rubber-coated-neodymium-magnet

Threaded inserts (M3x3, Qty 3):
https://cnckitchen.store/products/heat-set-insert-m3-x-3-short-version-100-pieces