HI
Make sure you put a inline fuse on the positive lead, as close to the battery as possible
if it get trapped for any reason, it will pop the fuse, otherwise it will catch fire
these leads should be supplied with a inline fuse
Ive used CTEK smart chargers for years and can be left on long term, anything above 3amp ideally, CTEK is what all the manuafacters use, Jaguar, Aston, BMW, Porsche, Rolls Royce. I use the Jaguar CTEK in mine, as it comes with a dedicated socket for the boot, so you just plug it in without the need to move anything.
Also the Jaguar CTEK is fully automatic, just plug in and go, no buttons to press, if you get a power cut, it just starts again , no need to go back in and press any buttons.
cheers
Joe