The magnetic door catch is very well made and finished but I don't think it will stand up to your marine climate over time. But you could use it but check it periodically for rust or other climate related wear. The catch itself is well made so I would try it out.
I’d say yes if you’re using the supplied screws. The instructions are clear and worked for me.
Don’t use the anchors.
Try attaching it to the baseboard.
1 inch long from end to end. The package comes with drywall inserts if you need them.
Stick a pair of needle nose pliers into the two holes of the backing plate and unscrew it.
They appear to be powder coated. I'm not sure if you can find a paint that will stick to that kind of coating - maybe car paint? Might work.
The magnetic door stop is not recommended for outdoor use as rust will occur.