TS
We use Marine 1500 watt inverters in out groups vehicled. All the trucks have bed liners and hard flush covers. I mount them in the right rear side on a wood base and I use a marine battery switches like -Series Mini Battery Switches.
http://www.westmarine.com/webapp/wcs...classNum=50547
If you do not have a positive cutoff your battery will die if you park for 2 weeks. We also mount them in trunks and in the cab if the truck has room like the cab and 1/2's do. For them I make a 1/2" plywood box to protect and mount them. If we are going to run a lot of things we put an extra battery to the system.
It all depends on the work needed. 400 watts are a little under powered for me.