I never had 12x2 brakes that were worth a hoot and I tried everything. The 7k, 5 bolt complete back plate will replace the 5 bolt 5200 and 6000 plates and they are supposed to have bigger magnets and more aggressive lining but they did very little good. Then I took an old set of shoes to a brake shop and got their best riveted lining, doubled up on the brake wire to eliminate the light gauge wire inside the axle tube, assured the magnets actually got full voltage and amps and the braking still sucked.
The only person I know that is happy with the 12x2 brakes on a heavy RV has a toy hauler that's lighter than my 5er and his TH has 3 axles/brake sets.
I've had smaller RVs (8400 gvw or less) with 10x2 brakes that would easily lock the wheels but a 15k lb RV with 4 drums no bigger than what's on an old car doesn't cut it!
13"/8k discs cured my braking problems. Craig