C-Tek MXS 5.0. I connect to a power socket on an external wall via a 15m extension lead into the boot of the Gransport and close the bootlid without any problem.
Same with the Porsche, but for the front bonnet where the battery is located. Shuts fine, no problem.
Both are always connected to trickle charge and keep the battery topped up. I leave them on it connected for six months when the cars are SORN'd October through to end of March. No problems whatsoever.
When the cars are on the road for six months, always kept on C-Tek in case I don't drive them for a couple of weeks.
I never believe anyone that asserts this fries the battery or kills it. Never experienced such phenomena.