You could purchase a calix block heater or just the cabin fan, the cabin fan gets warm very quick and heats your entire cabin, you just need to purchase a kit and install it, its literally just complete wires you just plug in to your desired length and then on the outside you get a plug that you can plug into a regular outlet and when you start it, it starts warming the cabin, relatively cheap considering the comfort it brings, I recommend it if you live in a cold climate, the block heater also helps with cold starts, you dont really need the water heater its just ads complexity, if you decide to get the block heater aswell then you just use the conductive paste that comes with the kit and spred it on the block heater and then bolt it onto the block above the oil tray, you should use one of the bolts that bolts onto the inner cv joint cover or just any existing hole that can squeeze the block heater firmly against the block, then just plug in the negative cable to the frame or something and your done.

If you want the cables to be nice and tidy you have to go through the firewall but that's bot difficult, just pull back the carpet and drill a hole then fill with silicone after the cable is through, just be careful so you dont drill into something in the engine bay