I have a storage compartment on my boat and didn't want to mount anything permanent. I had the idea of an 1/8" piece of Plexiglas held in place with rare earth magnets. I've done a little Google searching and no good information has come up. I have a lead-acid deep cycle battery and a 3 bank charger in the compartment itself and a Lowrance unit nearby. The Lowrance is about 2' away and about 3-4" from the battery, and charger. We're only talking a couple 5/8" diameter r.e.m.

Any cause for concern?

Not at all.The Lowrance is the only possibility and being 2' away is completely isolated.

Turned out pretty good. I caulked magnets to the inside of the compartment and to the outside of the plexi. That way if I take it off it's a clean look with no holes.

One thing I didn't consider is the NMEA2000 and Ethernet cables that run the Lowrance unit are right there, I'm hoping that doesn't mess with the unit. I'll cross my fingers and let you know

Looks good! There is no problem with the cables.