I've had those days, get everything packed up and set aside so I can go flying, head out and when I arrive it's absoloutely crap out, I remember that one time it was cloudy, but I started to setup and I just got the plane in the air and it started to rain, I just flew anyway, hunched over the TX so it wouldn't get soaked. I do use the edge of one 3/4" mdf board as a sanding edge, just line the part up on the edge and sand until the sanding bar hits the edge square. As far as glue, I tend to setup a "wet joint", liberally coated with glue and wipe away the excess and use a small paint brush to get the reminant, but I still leave a small fillet of glue. Just don't leave the fillet on the ribs where the sheer webs will sit, otherwise you'll be sanding a bevel in the webs to get them to fit tightly. I think the straight edges I bought at home cheapo, it's a adjustable T square that has a lockdown knob, I just unscrewed the knob and use them independantly, they're made of 1/4" aluminum and fairly heavy. As far as the pins, I stumbled apon those about 1 week ago in the hobby shop, I have no idea who the manufacture is, but in packs of 50 for for something like 3 bucks, and they are thin shaft pins too, I was sold. Bout 100 and it makes returning them to the container easy. I definatly want a power sanding unit, the kind with the vertical disc and belt and a adjustable table with fence to get correct angles and keep them square. Most of the 1/8 x 1/4 balsa was cut using just a single edge razor blade, just lined up the stick on top of the tail feathers, lined up the edge of the LE or TE and made a little push to get it started, then take it over to the cutting surface with the blade still stuck in it and continue to cut all the way through, looking at the side as you go to keep it going straight down. Sometimes I screw it up and have to knock it down with the sanding bar so it's square, not a biggie though.
Well, I got side-tracked and forgot to join those sheets and now I'm ready for the LE on the wing and the sheer webs too, so I'm going to get those done right now. I'm glad the pic's help.