If you have a some devices that need a mains supply to charge them, then a separate battery and inverter is one solution. especially if the existing 12V system has limited capacity and is otherwise functioning perfectly well.
If you can charge by connecting the MH to mains hookup, then you could wire it in (semi)permanently, with terminal eyelets and an inline fuse for the charger wires.
Just in case you don't know this, at the back of most 4-way mains extensions are two keyhole-shaped holes. You can use two flat-head screws into a wall or cupboard, and hook the extension onto them. If you adjust the screw projection just right, the screws will hold the extension quite well. Not as good as proper fitted sockets, but good enough.
Another thing to consider is that a high-power inverter has quite a high no-load drain, and also can be very inefficient for low-power loads. It is best switched off unless it's in use. May be better to get a small 150W inverter for powering long-term low-power loads like iPad charger.
If you can charge by connecting the MH to mains hookup, then you could wire it in (semi)permanently, with terminal eyelets and an inline fuse for the charger wires.
Just in case you don't know this, at the back of most 4-way mains extensions are two keyhole-shaped holes. You can use two flat-head screws into a wall or cupboard, and hook the extension onto them. If you adjust the screw projection just right, the screws will hold the extension quite well. Not as good as proper fitted sockets, but good enough.
Another thing to consider is that a high-power inverter has quite a high no-load drain, and also can be very inefficient for low-power loads. It is best switched off unless it's in use. May be better to get a small 150W inverter for powering long-term low-power loads like iPad charger.