I'm literally building a new trim tab for my RV-7 as we speak. It's one of many pre-paint items I'm taking care of. There's a tiny "crimp" in my original trim tab's trailing edge that I've never been happy with (that, and I can't keep away from making aluminum shavings on something).
I know some builders back rivet their trim tab spars. While I guess that's possible, I personally wouldn't want to do it that way. There's enough springback in the skin that you need to (at least I need to) over-bend the trailing edge to get the right bend/shape. With the spar in place while bending, I honestly don't think you could get a proper bend.
The pop rivets really aren't that big of a deal, but my new trim tab has all solid rivets. On the horns I used a 4" thin-nose no-hole yoke, and on the bottom spar rivets I used a longeron yoke with a relatively "tall" flush rivet set (somebody else mentioned using shims/washers -- works equally well).
You will probably want a longeron yoke eventually. My 2 cents is -- just spring for the stupid thing. You'll use it more than you think!
Oh...and BTW...I chopped the ends off. My end flap bends came out just about perfect on the first trim tab, but I no longer have the male/female wood V blocks around. So I chopped 'em off and I'm going with foam/glass to fill the ends perfectly flush. I had no idea how to deal with composites when I started my RV-7, and now I do.
