First, you will need a vent in the roof of your Airstream or Argosy, either powered or not. If you've got one, you can move to the next step, which is selecting the replacement vent that's best for your needs. There are several to choose from, both from the Fantastic Vent people, and Maxx-Air. In order to avoid any confusion, we'll deal with installing Fantastic Vents, though the Maxx-Air vents are similar in installation. All fit in a standard 14"x14" square vent hole, so out first task will be to remove the old vent, and prepare the spot for the new one. You'll need some tools, such as a drill (either electric or cordless) with a screwdriver bit, some wire cutters, hammer, a sharp chisel (a wood chisel will work for this), wire strippers, wire crimpers, tin snips, and a caulking gun. A ladder will really help as well.
First thing you'll need to do, is remove the interior vent cover, light fixture (if equipped) and screen. You will have to disconnect the light wire power lead when you remove the fixture, but it's a simple matter of unscrewing a single wire nut to take it apart.
Next step will be to wrap a towel around the spots on the ladder that will contact the side of your coach, and climb on the roof, being careful to stay off the compound curve end segments and staying near their lines of rivets in the roof. At this point, you should have your hammer and chisel with you, because you're going to be placing the sharp edge of the chisel against the edge of each rivet that holds the vent to the roof. There are a bunch of them, so it's important to find a rhythm, and go to town. Just follow the rivets around, until the round tops of the rivets are sheared off, and all you can see of them is the shaft going through the vent into the roof. While you're doing this, I'll go get a cup of coffee...
Okay, now that you've removed those rivets, and hopefully didn't remove any fingers or thumbs in the process, we can move along. Using the chisel, wedge it under the edge of the vent, and lift up on the chisel. When that part of the vent starts moving away from the roof, go to another spot on the vent and repeat the procedure until the vent is loose all the way around. Carefully lift the vent out of the hole, and, depending on your personal feelings for it, either carry it off the roof, or throw it into your neighbor's yard. Trying to hit the neighbor with the vent is optional, and depends on your relationship with your neighbor.
Now that you've disposed of the old vent, it's time to prep the hole in your roof so it will accept a modern replacement. If you look at the hole, you'll notice it has radiused corners that will need to be squared off for the new vent to fit. You can cut the corners square, and test-fit the new vent. If the holes in your roof are a bit too small, you can trim them out with the tin snips as well. Before final placement of the new fan, you'll need to clean off the remains of the old rivets in the roof, and scrape the old sealant off as well.
Fantastic supplies a foam gasket for the base of the replacement vent, which works well on the fiberglass and rubber roofs typically found on RVs, but Airstream products respond better to Urethane sealant, best known under the trade name Vulkem. If you came prepared for this job, insert your tube of Vulkem in your caulking gun, and run a bead of Vulkem around the hole in your roof. If you don't have a tube hanging around, you'll need to go to the RV supply store and pick one up. I'll have another cup of coffee while you go.
Now that you're back with your Vulkem, and have applied it to the hole in your roof, you are ready to place the new vent in the hole. You'll need to be sure you place the vent with the hinge of the lid facing the front of the coach. You now can install the mounting screws that came with the vent, using the screw gun attachment and your drill. Run the screws down until they are snug against the vent, but don't over-tighten them. Now run another bead of Vulkem around the outer edge of the vent, and a small blob of Vulkem over each screw.
Now that you're done on the roof, you can go inside and complete the install. You will need to use the tin snips again to enlarge and square off the interior vent hole, like you did on the outside.
It's now time to wire your new vent, which is pretty straightforward. The black wire for the Fantastic is power, and will go to the power lead from your old vent fan or light fixture. Crimp the wires together, and that part is done. You'll notice a white wire on the vent, which is the ground wire. Fantastic and Maxx-Air vents are non-metal framed, and need the extra wire to ground them. Strip the end of the wire, and crimp a ring terminal to the end. You can rivet this to the ceiling panel, inside where the interior garnish will go. If you don't have any rivets, you can use a sheet metal screw to perform the same task.
After testing the fan to make sure it works properly, you can install the interior garnish with the 4 provided sheet metal screws. You will probably have to trim the garnish so it won't protrude below the ceiling.
Now you can invite all your friends over to see your new, much-higher-flow fan.