The two wires pull off terminals on the igniter button. The propane hose to the burner just pulls straight off once you pry the clip off (don't lose the ciip!). At that point, you can remove the entire kettle from the cart with four large philips head bolts. Disassembling the cart depends on whether it's a late model or older model Performer. If it's a new one, the plastic table comes off with four more Philips head bolts. Then, you could unscrew the plastic strut on one end and lift out the wire shelf. at that point, you'll be down to two tubes -- front and back, which should be as far as you need to go.
If it's an older model, I'd do everything possible to transport the cart in one piece (after removing the kettle). The metal inserts at the end of each tube on the cart are what ultimately rusted and killed my old Performer. Removing the bolts that hold the legs together, unless absolutely necessary, could be opening a big can of worms. Rusted/stripped bolts on the cart are going to make you swear and/or write big checks to the Weber parts department. Strap it to the roof if you have to!