Nice and clean install! Magnets are too iffy for me, I prefer to keep and use the 3M tape that these bars come with.
I installed (five times LOL) the 60" Recon Xtreme and have never had a problem with the bar staying where I put it. The 3M tape has proven itself through all imaginable weather and driving conditions. I also didn't need to remove the tailgate - as someone else already mentioned, the mounting location can easily be marked with masking tape with the gate down.
Again, nice install.. hope the magnets hold up for you!