I've used them for more than 25 years. I actually had an old "vibrator" inverter in my SIII Land Rover back in the late 70's. Since I'm just now starting my equipment install in the G, I have none permanently mounted there. However, I've had a 600 watt inverter in my Rangie for about 10 years, and used it a LOT! I pretty much find it's hard to go without it now.
In actual use, it's rare that I draw more than a hundred watts. Usually for laptops, radio and tool chargers or other instruments that are temporarily installed in the passenger seats. Although I have on several occasions plugged in work lights and fans.
As for the installation itself, I personally always install a disconnect solenoid which is controlled by the accessories switch via a battery level sense controller. This also provides power to the radio transceivers too. This automatically disconnects all of the electronics during vehicle starting, which does double duty 1) allows max power for starting and 2) prevents voltage spikes from the starter damaging the electronics. This last is pretty important in the long run, considering that the vast arrays of power transistors in the Inverter and in the radio transmitters are permentently connected to the 12v input line. Also, using the disconnect solenoid prevents any chance of small power drains from the equipment running down the battery.
For wiring, last time I ran #2 welding cable via 3/4" liguid-tite flex conduit under the truck to the inverter/radio in back. Other essential upgrades were a 150 amp Delco 21SI alternator. I absolutely always put a main fuse right at the power feed from the battery circuit, and usually a power distribution box at the equipment in back, after the solenoid. I've found that marine power distribution boxes work pretty well for this.
As for the inverter itself, I've been using modified-sine wave inverters. These are dirt-cheap and reliable, however they have the very bad side-effect of producing considerable low-frequency emissions which can wreak havoc on HF radio reception. I suspect I will install a 1kw pure sine wave inverter in the G.
Something else worth thinking about is safety. Most all power inverters have a completely isolated ground output. This is good and bad. Good in that it's safer for a mobile environment, kind of like a permanent GFI, but bad in that sometimes strange ground-loops occur when they shouldn't. Probably due to the capacitive coupling in the output circuit filters. More than once I've had my face stung by metal-faced cell phones plugged into chargers running on the inverters.
As for my impending G installation, I'll be posting on here how it finally ends up. It will be completely different, as the G is representing a significant challenge. It is so much tighter-built in every respect than most any other truck-type vehicle I've worked with. Finding room for things is difficult, especially in the engine-bay. Getting a big alternator in there will be a challenge, and I guess I'll have to forget about dual batteries. But I will make it work.