For wing rubber band dowels, I've gone to using 1/4" solid fiberglass rods. You can get them at kite supply places like kitebuilder.com or your favorite source for composites. The fiberglass rods won't break for nothing, which helps keep the wing on in hard mid-airs. I used to use 1/4" hardwood, but the dowels broke way too often.

I like the sliding bracket. Is that just for setup, or do you want to fly with it that way? If you fly with it that way, I'd put the wing rods under the metal rails. That does mean you'll be landing on them, but they can take it. Or use a metal hook system like a lot of guys use on that type of fuse. But I'm not sure I'd rely on that metal bracket to hold shape in very high-Gs, and especially not in a mid-air. So I'd make sure that the wing is holding directly to the rails, and the bracket is just there to keep the box from moving.

Also, you might think about a way to keep the box from flying forward on a nose-first arrival. I've seen a number of Axe-style planes punch holes in the fuel tank as the box comes forward, pushing the tank and throttle servo together and into the engine. Often times, the plywood wing saddle box dies in the process as well, but it kind of depends on exactly what hits what. In any event, look at what will happen should the fuse do a lawn dart, and see if you can reduce damage.

about the size of your plane, it's not small over all for a .15, but I think your wing area is a little small for a competitive SSC design based on what I've seen. The problem comes from the SSC rules requirement of a minimum weight of 2.5lbs (40oz). At that weight, and the intentionally limited power, SSC planes need to have a light wing loading to perform well.

Speaking of which, I can't tell from your pictures what your wing saddle looks like. If you have a flat bottom on the airfoil, make sure you aren't setting the flat part of the airfoil down parallel to the metal rails. Doing that gives you a ton of positive incidence, which you probably don't want. You'll probably want a little negative, maybe a degree or two.

The good news is that the Clark Y has fairly nice stall handling.

btw, I meant to ask earlier, you said you used the Clark Y, was that the actual Clark Y template from an airfoil library, or do you just mean a generic flat-bottom airfoil? A lot of folks in RC models seem to call anything with a flat bottom (like on many trainers) "Clark Y", even though it isn't actually the Clark Y airfoil.