Disconnect the negative first. Reconnect the negative last.
When removing or isolating a battery, you should disconnect the negative wire FIRST. This is an old Fire Department trick, which makes sense; if your wrench accidentally touches chassis ground, and you're on the ground wire, there is no spark because there is no voltage difference. Once the negative is disconnected, you can work on the positive wire, which no longer has a battery connection path to ground (because you disconnected the other side of the battery) so there won't be a spark there either. So ALWAYS disconnect the negative FIRST, and reconnect the negative LAST.
But there's little reason to disconnect the positive red wire if you're just isolating the battery for storage. If you leave the positive connected to the battery, it won't have any chance to touch chassis ground. No need to try to insulate it at all, it's as safe staying on the battery as it was when both wires were connected. Just disconnect the black wire and put it where it won't touch the positive post.
But now you have to ensure your AC battery charger or solar charge controller wont try charge a battery that's not there. With no battery, it can overvoltage anything still connected to your 12 volt house system. Shutting off the battery charger is easy, there's usually a AC circuit breaker for that. Disconnecting a solar charge controller is a bit more effort. Ideally it should have a fuse which you can pull, or it might have a wire to the battery you can disconnect, or it may go through the 12 volt power distribution center, or wired somewhere else. But many charge controllers need the solar panel inputs disconnected before the battery is disconnected, which is an additional step (and battery connected before reconnecting the solar panels).
The remaining charging source is the alternator, which is kept in regulation by the starting battery. It will not overvoltage your house accessories unless the starting battery is removed while the engine is running (a very unlikely scenario with RVs).