A recent flurry of rack-building activity resulted is a nice sampling of various approaches to attaching a small rack to a fork, and stabilizing the bags that go with such racks. There's a stream of six photos showing these recent racks and decaleurs that starts here.
Probably the most interesting, from a fabricator's perspective, is the rack shown below. The customer came to me with an expensive new custom (built by a well known Wisconsin outfit) that was intended to combine the center-mount brake with a rack that attaches via one of those "you-bend-it-to-fit-under-the-brake" center tangs. The execution had been muffed, the spec'd rack sat where the fender should be, and his fork simply didn't accommodate the tire and fender that he'd listed on the order form. One part of my solution was to build a rack that features a yoke that mounts on the brake's center bolt, sandwiched between the brake and the front of the fork crown. This took some doing to fly the rack's deck tubes around the brake's working envelope, away from the crown's protruding shoulders, and into the yoke. But it turned out very nice. And, although this was designed around the Tektro R538 sidepull brake, we also know that it works equally well with the new Paul's Racer-M center-mount.
When it comes to stabilizing the bag on these front racks, I believe that there's a valid structural design argument for not using an overly tall backstop supporting an integrated decaleur fixture. Instead, I prefer a design with the decaleur's root placed high and forward, and with short lever arms that carry bag-generated bending forces. The decaleur shown below mounts to a stem with a 4-bolt faceplate, and incorporates my design preferences. With a modular design like this, individual elements can be replaced to fit other bag/stem/rack combinations.
The photo below shows this decaleur design in use. The spine piece is bolted directly to the bag. The linkage is created by inserting the L-shaped retaining pin, which, in turn, is locked in place by the little R-clip. To release the bag, simply remove the R-clip and slide out the retaining pin.
With this particular frame/stem/bag combination, the bag support hangs from the stem on short struts, rather than by the long cantilever arm found on aftermarket steerer-mounted decaleurs. And these struts are easily positioned using bolts, not by bending the structure. My design may weigh a bit more than something integral to the rack, but, as one customer described it, it's "sturdy as all get out". That's the idea, no?