Quick follow-up on the fender cover I ended up choosing. I ended up getting one from FCP Euro made by GearWrench (the one recommended by (K) above):
https://www.fcpeuro.com/products/fen...arwrench-86991
I like it pretty well. The magnets hold it place on the fenders quite securely. The "tool trough" on top is deep enough to keep tools in place (and the extra tool weight further anchors the cover in place). It's thick enough to feel like it's doing a good job protecting the paintwork from spills and drops.
If I were to offer a critique: I wish it were every-so-slightly taller so it would cover more of the car. This is especially when I have it covering the front bumper cover as I lean into the front of the engine bay.
And definitely on the plus side, I got this from FCP Euro: when it cracks/rips/ages, I'll just put the the lifetime replacement policy into action.