First you need to rivet the ribs to the spar. This is nearly impossible on five out of six ribs. The problem is a really poor design on Van's part. Basically the leading edge ribs and main ribs are offset horizontally from each other by about a half inch. This, however, doesn't really give you much room next to the main rib web to get a rivet set in there. As you can see in this [horribly fuzzy] picture, even a double-offset rivet set can't be seated straight onto the rivet head. In the picture, the gray on the lower right is duct tape to protect the rib web, and the stuff in the middle hole is the back end of a cleco. Tough to make out, but the rivet set doesn't sit straight on the rivet head.
What I ended up doing, besides freaking out, is calling Van's builder assistance line. The guy was pretty helpful, although their solution is pretty crummy. They recommend you grind/file away enough of the rivet set to get it to seat at the right angle. And if you just can't do it, use an LP4-3 blind rivet. Straight from the horse's mouth...these rivets aren't super-structural, they just help keep the spar from buckling, which is basically a zero chance thing anyway. I was surprised at the nonchalance of Van's recommending using a blind rivet, but it does make sense.
Anyway, I ground off much of the rivet set, quenching it in cold water every so often so as not to change the temper of the steel, and I finally got it to a point where it would sit properly on the rivet. What a waste of a good tool. But it worked for the most part. I shot and Jen bucked the first (inboard) row of rivets. They actually came out fine with no smiles or anything.
Getting all cocky, the next row was a completely different ball game. There's no way to get your arm in to buck the rivets other than through the lightening holes, and access sucks. So we skipped ahead to the next rib, which is better and worse. First, there's a small lightening hole in the spar web, but it's just barely big enough to get your hand and wrist through. Jen just couldn't manage shooting properly, nor could she figure out the bucking situation. She's a great flush rivet surface rivet shooter, but she kind of sucks at these funky orientations. And she had a hell of a problem with trying to work blind on the bucking side. We smiled and slanted a few rivets, and then she gave up. I drilled them out.
Here's a shot of one of the rows of holes which has decent bucking access (through the holes in the spar) but terrible shooting access.
Anyway, I deliberated a while about this, and ultimately I decided to go with the blind rivets as Van's suggested. I took my already-ground-away cheap-ass rivet puller, and I ground off even more of the head so it would sit against the rib web and approach perpendicularity with the rivet head. I got it to a point where it worked and I ended up putting LP4-3 rivets in the rest of the holes.
Except for the very outboard row, which I managed to squeeze with a hand squeezer and a normal 3" yoke. This was the most pleasant note of the process...
After the rib-to-spar ordeal, the skin to spar riveting was a freakin' breeze. Within about 20 minutes, the leading edge was completely riveted on. Look ma, no clecos...
Next I went on to the "scarf joint," which is where the top skins overlap around mid-span. I clecoed the top skins back on. Plans call out filing the corners down so that they lay flat relative to the tank skin. I did most of this with a sanding disc in my die grinder, followed by fine polishing with ScotchBrite. Worked pretty well.
I need to prime these surfaces before riveting the skins on, but that's pretty much next. I really oughtta work on the tank...