Tonneaus, tonnos and lids are all words for essentially the same thing: pickup truck bed covers. In fact, "tonneau" is the French word for "cover." Tonneau covers came about in the late 1970's. Before that, the closest anyone came to the present-day tonneau was a plastic tarp. Nowadays, tonneaus range from expensive, durable, custom-painted fiberglass lids to low-cost, affordable frame-mounted vinyl covers. These covers serve a variety of purposes, including protection from the elements and theft. Your hauling schedule will not be contingent on the weather when you have a pickup truck bed cover. You'll be able to transport on your own schedule instead of mother nature's. Of course, your hauling capacity will be somewhat limited, as tonneaus obviously do not create vertical cargo space like camper shells. They do, however, provide a strong, rigid canopy over the pickup's hind end, while maintaining a low profile...especially hard truck bed covers. Most models don't restrict the tailgate, so you'll be able to open and shut it without fussing with the cover. Essentially, you'll have created the equivalent of a very large car trunk. Most tonneau styles will work with both under-the-rail and over-the-rail bed liners, and don't require drilling into your vehicle.
Besides the obvious practical applications, pickup truck bed covers are a quick way to substantially increase the appearance of your truck. You won't have to look at and be constantly reminded of your scratched-up bed. No one else will get an eyeful of the load of junk you're hauling around in your Dodge truck bed. Cover it up, and it may as well not exist. (That holds true for potential thieves, too.) Also, you'll be adding value to your truck. In fact, the Kelley Blue Book indicates that a tonneau can add anywhere from $100 to $200 to a truck's resale value. Just one more good reason to accessorize your truck today.