Random points....
--Full HARD fairings on two-wheel bikes are extremely difficult to handle in crosswinds; most people experienced with them feel that such devices are NOT useful for a bicycle used on the street--just because of the crosswind danger (-a "hard" fairing is one made of essentially rigid material-).

--The two "main" recumbent fairing companies are Zzipper and Windwrap. Both companies products offer roughly comparable products, and both will sell the bits and pieces separately if you're doing a D.I.Y. job. These are polycarbonate plastic sheeting heated in ovens and blown. ....You see on the Zzipper home page, a fairing for the RANS Zenetic, which is a semi-recumbent. Some of these fairings could probably be fit onto upright bikes the same way.

--What many recumbent riders do to cut wind drag is use a front fairing (from Zzipper or Windwrap) and then use a body sock. A special rear rack is attached to the bike, and a lycra sleeve is stretched between the edges of the front fairing and the rear rack. Although these look kinda silly, they can have almost as low drag as a hard fairing, and have some "give" so they're not so dangerous in crosswinds. They are also lightweight, and relatively cheap and easy to make if you've already got the front fairing.

--Front fairings do cut drag, typical is they ad 1 to 1.5 mph onto a 16-18 mph cruising speed but they also add weight. People do use them in hot climates, but it seems like most people who buy them do so partly because they live and ride in cold weather, and using a front fairing drastically cuts wind chill that the rider feels.

--Regarding tailboxes, there's a few upper-end companies that offer them for their bikes (recumbents costing $3000-$4000+) but a lot of people make them out of corrugated plastic (often used for cheap small signs). Search Google or Google images for the terms "recumbent coroplast", and you'll get pages of people who have done home-made fairings. Some look cheap and silly, some look impressive, most are in-between.

--It is true that drag happens behind objects and not in front of them--but even so--informal experiments generally show that adding a FRONT fairing helps more than adding just a tailbox. The one exception to this is that lowracer recumbents (like the Velokraft NoCom) generally aren't fitted with front fairings, because for the fairing to be effective the rider's body must be placed relatively close to it, and with the stretched-out designs of lowracers this isn't possible--so such bikes like the Optima Baron (another lowracer) are commonly seen fitted with tailboxes, but rarely ever are used with front fairings.
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