Samlex Inverters are wicked, Pure Sine only is the way to go. Just put a 1000W in the bed of a customers Dodge for all his ski bags and whatever else he wants to throw at it, he loved it and I loved it so much I must get one now too :). We didn't use their optional panel they ship with it, just wired it to ignition power so it won't kill the battery if someone "forgets" about it.
If you have a ton of accessories, a dual battery setup can help or an upgraded alternator may help as well. Don't run a cheap battery either as you stated, Optima are good and Interstate own's them, I love my Interstate batteries, call them up and give them the size(s) you can fit and find some big buggers to put in there :)
Good luck! Keep us updated.