Mounting the hardware is a good idea if you plan to move your cab. If you want a cool way to mount, check this out:
I mounted the side panel of my new PC case to the inside of my cab's back access door using 6 wood screws (reinforced with finishing washers.) Make sure the door is mounted so that the case won't hit any monitor shelf etc, and that there is enough room at the back for cables when the door is closed.
Now the PC case is easily attached/detached by sliding it onto the side panel hooks. The PC is secured in place with a single brass case thumbscrew.
This arrangement allows easy access to the front of the PC buttons, drives and the front panel USB by opening the back door just a few inches. The height of the PC makes plugging/unplugging cables easier. The only drawback is that the case must be unmounted and all cables unplugged if you want to get inside the case to upgrade hardware etc, but this is infrequent enough, and it only takes a few seconds to pull all the plugs and unmount the PC. So far, I love the setup!

BTW, this is called the "Neon Blue" case and is a common offering on custom PC sites found on pricewatch. I got it from TufShop.com.
This case SUCKS! It was supposed to come with a neon case light. Uh-uh. The light was missing, the case and side panel were heavily dented, the blue front panel is broken loose on one corner, and when I opened it, all the screws were pouring out of the ripped screw pack. Despite this, there was no damage at all to the box it came in... Worst is that I paid $60 for it!!

It is also made from the thinnest metal I've ever seen this side of a Pepsi can, and even the panel the motherboard mounts to is easily bent. The upside of this is that it is very light and easy to mount. Oh well...