I think the Tubus racks would be stiffer and stronger than this RockBros rack.
And I've seen adapters that fit under the rear caliper brake bolt if you don't have upper eyelets.
At
TheTouringStore.com, you can get the 800 number to call. You'll reach Wayne, the owner, and he has extensive experience with making racks work correctly on all kinds of bikes.
Unfortunately, he's temporarily closed until the end of May. But check out his
rack adapter page.
When I ordered my Tubus Logo rack from him, he asked a couple of questions, and immediately knew I needed a small aluminum spacer to fit my rear wheel dropouts, and knew that the rack would easily fit with 40c tires and fenders. Very helpful. So if you can wait to the end of the month, he can probably get you working.
It's often easier to
attach the rear fender stays to the tubus rack, instead of the bike frame. There's often a little more room that way. The tubus racks have holes for this purpose (but they aren't threaded, you need a bolt, washer and nut, usually a locking nut with the nylon insert. These are available at your local hardware store. I got the stainless bolt, nut, and washer, and found some 1/4 inch thick nylon spacers that kept the stays away from the rack tubes.