Popping in a new headunit isn't hard at all. Running the wires cleanly, securely and properly is just time consuming. I solder all connections then use heat shrink tubing. I also use an adapter for the stock harness so I don't need to cut anything factory in the cruiser and I can return the system to factory in minutes.
Step one: Yank out the dash control panel, it just snaps in.
Step two: Run your wires and cables in the right places.
Step three: Button it up.
Okay, it might be a little more involved than that but not too much. I did make a custom harness with the JVC/Toyota combo and needed to solder about 20ish connections there. Otherwise, it's plug and play.
Here's what you start with:
Slowly and carefully tear the insert out!
Disconnect the AC controls...
Unscrew the 4 bolts holding the factory Head Unit from the dash and remove the brackets so you can slap them on the new stereo.
Attach the brackets onto the new Head Unit. Snug them up but don't crank on them.