John,
I've got the same drum sander, and I've struggled with the "tool" (using the term loosely) that is used to lever the springs which clamp the sandpaper down. Getting the paper on absolutely tight and flat is critical. If it isn't, I've found that the drum sander will
1) make an awful racket,
2) take gouges out of the wood, and untimately
3) shred the paper, sending bits of paper and grit everywhere. 
Won't see you at Blues Creek tomorrow - have a camping trip with my 6 year old.
Here's what I do to get the paper flush.
1. anchor it on the left side of the drum, make sure it's gripped properly under the spring clamp.
2. Roll the drum by hand, paying attention to tightly wrapping the sandpaper, with no overlap, but almost up tight to the last wrap (1/64th of an inch gap?)
3. When you've wrapped it up to the other side, you should have the right amount of remaining "tab" to insert in the right side clamp. Too much and you've probably wrapped the paper with too much gap between "wraps". Push it in the clamp by hand. Now the tricky part, and I found that the directions do indeed, suck. I'll try to describe what I do.
4. Take that tool, and insert the hook in the hole on the right spring clamp, from behind. Pull it towards you, and twist to the right. This will lock the spring in the open position. Make sure the paper is totally tight, and flat to the drum. Twist the tool back to the left, releasing the spring, as you hold the paper tight and flush. If there's still a little play in the paper, you can use the tool to release the spring just a little, to push the paper flush.
Hope this helps. I've also found with this sander (and probably others) that you can't go too fine on the paper. 120 grit, for example, is almost worthless - it clogs with sawdust, and creates high spots which will burn the wood, rather than sanding it. I use 80 grit for most everything when thicknessing, and take small amounts off with each pass.
All that said, I do like the tool and find it pretty accurate. If after this, you're drum is still not level, perhaps someone else on the forum can help. I've not had to level the drum - not sure the process. Good luck!
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