We used to put paper on foam wings with a thin mixture of water and white or yellow carpenter's glue.  After a couple coats, it was fuel -proofed with a spray coat of some kind of varnish like Crylon.

Then we discovered Solarfilm and other low-temp plastics and increased production.

Obviously, different people are using different techniques, but here is what I do. The assumption is that you will be putting some type of film covering on the wing OVER the silkspan, be it something paintable like SLC, or something pre-colored like Econokote. I will also assume that the wings are glued onto the fuselage, the spars are installed, the filament tape reinforcement is applied, the wingtips are shaped or installed, and that everything is sanded to your satisfaction. For this discussion, I will assume you are using solid balsa tips as per the Sniper or Hellcat.

First, either vacuum the wings or blow them off with compressed air to remove any sanding dust. Next, cut the pieces of silkspan to size. I find it easier to cut the silkspan to the appropriate size ahead of time, rather than try to trim wet silkspan on the airplane. I will use the foam wing "shucks" to determine the size. Cut the silkspan to match the length of the shuck, and cut the chord about 3/4" wider than the shuck. Maintain the correct leading and trailing edge sweep so you will have a nice even overlap. Note that there will be covering overlap on both the top and bottom surface of the wing when you are done, helping to strengthen the leading and trailing edges.

Next, spread out a bath towel on the table. Take one of the pieces of silkspan and either run it under the faucet or spray it down with water. Blot it on the towel to remove excess water, then lay it in position on the bottom of the outboard wing. Position it to achieve approximately equal overhang at the leading and trailing edge, and butt the root end up against the fuselage the best you can. Since the silkspan expands when wet, there should be some overlap onto the balsa wingtip as well.

Now, with a 2" foam brush, paint a mixture of 1/2 carpenter's glue and 1/2 water onto the silkspan. If you mix the glue in a cereal bowl or butter tub, it will be very convenient to apply. As you are applying the glue, occasionally scrape the wing with a playing card. The idea is to remove excess glue, and smooth out wrinkles as you go. Excess glue will undoubtedly drip off, so try to do this over a trash can, or spread newspapers on the shop floor.
Once the silkspan is all stuck down, you may optionally blot the wing with a paper towel to remove a bit more moisture. I find it helps speed up the drying a bit. Immediately repeat the process on the top of the outboard wing. If the bottom is allowed to dry first, the shrinkage of the silkspan will warp the trailing edge. After completing the outboard wing, cover the inboard wing in a similar manner.

The next day, sand everything lightly with 220 paper. If you sand through anywhere, smear it with a bit of straight carpenter's glue. If you use the strapping tape reinforcement like I do, remove the silkspan from on top of the strapping tape. I usually just sand through the silkspan around the edges of the tape, and it peels right off because the glue doesn't stick to the tape. Again, touch up any problem areas with carpenter's glue.

Lately I have been covering over the silkspan with SLC covering and then painting the entire airplane. I am doing this to seal all the seams and keep them from lifting or getting oil soaked. So far it has worked perfectly. The only peculiarity to the SLC is that it doesn't seem to like wingtips very well. I will cover them the best I can, then slice off any wrinkles with a sharp razor blade. Then I will paint the wingtips with a liberal coat of finishing epoxy. It may take a sanding and a second coat of epoxy, but I have been able to achieve good results every time. I also paint the SLC seams with finishing epoxy and a small brush. Not only does this help keep fuel out, it helps keep solvents out so the paint doesn't dissolve the foam. At the fuselage, I apply Super-fil fillets over the covering, again to seal everything as completely as possible.

I have painted SLC with epoxy paint on one airplane, and dope on another. Both seem to be holding up just fine.
Earlier airplanes were all covered in traditional low temperature films, and despite my best efforts, started to experience fuel seepage at the seams pretty quickly. These coverings are quicker, easier, and probably lighter than painted finishes, and are more readily repairable. You decide what's best for your particular project.

I don't think I left out anything important. Please ask any questions.

I don't think you could get music wire to stick very well. A carbon rod would probably work better.  With two layers of paper wrapped around the trailing edge, I find it to be sufficiently tough. I have tried 1/8" square spruce, and even heavy string in the past, and decided it wasn't worth the trouble.

Scott, the end of May is closer than you think 

Here's a tiny bit of additional information. Somebody had asked about how much weight this adds. I just covered a new 360 sq. in. profile carrier airplane yesterday. I used medium silkspan on the inboard wing and heavy on the outboard wing, just because that's what I had on hand. It added 22 grams, or 3/4 ounce. Also, for the record, the entire process took about 45 minutes using silkspan that was pre-cut to size.

Just in case anyone is wondering, the SLC covering added 20 grams.