I don`t think you are missing anything from a safety perspective. But I would wire the stereo to a breaker (or fuse if that is what you have) and only run the memory wire to the battery direct. This will eliminate the risk of draining the batteries.
As for the tv, some are very voltage sensitive. 12 volts is what it requires but wiring around the power supply will give it as much as 14+ volts. Some tvs will tolerate this and some won`t. I also would not wire the tv direct to the battery. It should remember the channels whether powered or not.
Living aboard in Victoria Harbour