I have 3 QR's like what was pictured above. Just like TourMan, I attached them to a 2x4. The only difference is my truck's bedliner has slots to hold 2x4s. Since I made the rack, I have had only 3 minor problems.
1) I put the QR's too close together rendering the middle one unusable at times.
2) I forgot to put lock washers on one of the QRs. After a few drives, it would work its way loose. The other 2 had lock washers and have held fine.
3) When the 2x4 warped, it quit fitting into the slots correctly.
When I build my next one this weekend, I will make sure to make it so that 3 bikes can fit and to paint the board to prevent it from warping.
I post this so that if you make your own, you don't make the same mistakes I made.