Do you have or want a battery isolation switch? Do you want to be able to use the socket for charging the battery as well as powering devices? If I were doing this again I'd fit both a "cigar lighter" socket and a couple of USB ports. But NB the current capacity of the USB ports (they're not all the same!), and the possibility of the converter generating electrical noise which could adversely affect intercoms and, presumably, entertainment.As above: lots on this in the archives... Jonathan