You'll need at least a 5K generator if you're gonna run A/C on that Passport 40.
Figure at a minimum $7-8K for the generator, and about $2,500-3,000 for professional installation. Recommend you have the gen dealer install it, get a sound shield, and pay attention to servicing needs (location of water filter and water pump impeller, fuel solenoid, oil and filter change, brushes, etc.).
I've been happy with my 3.5KW NextGen. It will run one of my A/Cs OK, but I'd really like to have more power....no room, though.
Remember not to spec it too close. A 5KW genset won't provide 5KW continuously. As they heat up, output is reduced by 20-30%. Other things (like power factor of load, poor fuel, etc.) can also make them deliver less power than you'd think.
Last edited by btrayfors; 10-15-2008 at 08:16 PM.