The most important thing is getting the size inverter for your needs...but make sure you only use around 60% of it's total power...you don't want to run it at it's peak capacity.
The second most import thing is THE WIRING...if you try and scrimp to save money on small/inferior wiring....call your insurance company, and upgrade your coverage...because your truck will become a very expensive bonfire.
Power Inverters and Accessories by Cobra, Xantrex, Wagan, Magnum Energy, PowerBright, Samlex, Voltec, Whistler and Goal Zero - DonRowe.com - Index
^^^^ has all the info you'll need to correctly choose the size inverter for your application, and the info on the correct size wire to use....as well as ...they sell you an inverter...LOL
I run a 10,000 watt inverter in my truck,...I have 2 welding cables for power, and 2 welding cables for ground...
My daughter is my electrician...LOL
Like I said, that link will give you all the info you'll ever need on inverters...
You have to decide what you'll be powering to see what size inverter is adequate...
To figure out what you need, use this equation....AMPS X 120(AC volts)
A Circular saw...15 amps x 120 = 1800 watts...
BUT!!!...you also need to take into consideration of
"start-up load"...which is generally double the needed wattage.
So a simple 15amp circular saw, to run properly(not eventually burn out the motor), needs an inverter with at least 3,600 watts of power...
BUT!!!...as I mentioned earlier...you never want to run the inverter at it's max capacity...
15amps x 120 = 1,800watts x 2 (start-up) = 3,600watts....I would recommend a 5,000watt inverter.
OK...now wiring(though it is in the link)...1,500watt inverter.
3-6ft run = 1 gauge
6-10ft run = 3/0
I run a 10,000 watt inverter,...simply because I don't want to sit and do equations every time I want to power something....LOL...GO BIG OR GO HOME!
Besides...the inverter I got only cost about $450...so it was a "no brainer" for me