I've installed a bunch of Maggiolinas on shells. All the major manufacturers of fiberglass shells are good (SnugTop, ARE, Leer, etc). If I remember right, they shoot for a 300 pound rating on their roof, while truck is in motion. This means the shell can hold a multiple of this while at rest.
The tricky part is setting up the rack. Both Yakima and Thule have great solutions and you can go to most any dealer and they will install. You can ship your tent to them and they can also install the tent on the rack too. I've had some dealers balk at putting the tent on until I explain it is a 120 pound storage box and they they are cool. If you are near a "Rack n Road" store, they are really familiar with installing these tents, usually have a couple in stock. It isn't too difficult to do yourself if you wish to save some money. You get one of their "track" kits and follow the directions. I recommend getting the longest tracks that will fit on the shell, it gives you more adjustability to mount the tent. The concept is to spread the weight out, fiberglass doesn't like point loading much, it is a pretty flexible material.
One thing to keep in mind is that fiberglass is strong where it curves, the flat sections are the weakest, can "oil can". I've always liked "artificial raingutters" and raingutter style feet for your rack. I think this is the strongest system, bolts to the side of your shell. It is much more of a utilitarian look. My favorite is an obscure system called "Quik n Easy", they have die cast alloy feet and they also have stainless artificial raingutters. I remember getting everything I needed for less than $100. Don't use the Quick n Easy crossbars, go to a steel yard and get a couple stout square alloy tubes to use as crossbars. The system is then all alloy and very strong and light. NRS carries their stuff
http://www.nrsweb.com/shop/product_list.asp?deptid=1379
Oh, almost forgot, don't recommend mounting a rooftent on a plastic or a aluminum shell. The ones I have seen aren't really up to the task. Get a ladder rack and mount the tent on that. Adds a lot of weight but it is very strong. Fiberglass is really the way to go for shells in my opinion.
You can also talk to Mike at AutoHome, who imports Maggiolinas. Talked with him last week, he is off to the Idaho backcountry with a bunch of his customers. Should be back in two weeks.
Rich
