Using steel shingles from Home Depot, I use snips to get a straight cut, then a ball peen hammer to flatten out the crinkles (typically on the flat shelf of a vice). Prime the whole tray black, no problem. My movement trays have plenty of issues, but wrinkled metal is not one of them.
Fun fact, the shingles are 5" wide, so for all of us normal size armies, you only have to cut one dimension. This really helps with the straight lines.
Was this the one at WOW? I recall Plague Monks vs Saurus Warriors... Or another... I have a long history of disastrous 2v2s.
This is what I used for all my rats. I went through two phases: hot glue and epoxy. You have two problems with using neodymium magnets. The first is that you have to use small ones so you can, you know, remove your models. This means there will be a gap if you super glue it to the bottom of the base. The second is the strength of the magnets breaking things off. I used hot glue at first because it solved the first problem by acting as a spacer. However, after my first tournament I probably had 40 magnets (out of 200+ models) stacked up on my tray that had fallen off. At first I would just glue them back on. Hot glue is cheap after all. After a few years I got fed up with hot glue and started researching other solutions. I came across the plastic epoxy that I linked before. It is thick enough to space the magnet off the base and allow for better contact with the metal, and it is strong enough to not break off after a single use.
I still have to repair a few models before each tournament, but the numbers are way down from before. Most of the broken ones end up being hot glue that I never replaced. For example, this week I glued six magnets. Two never had them, two were old hot glue and the last two were epoxy.
One suggestion that I've seen but never followed is to scratch up the magnet before gluing it. The theory is that this will help the epoxy to bond to the magnet better. I have had plenty of success without this. Unfortunately all of my metal scratching tools are.. metal... and the magnets are small. I try not to cut my fingers as much as possible, so I skipped that step.
Last comment on the epoxy: it is decently expensive, but I have managed to do about 80% of my 300+ model army (as they break) and I've only used two tubes. The trick is to do as many models at once as possible so that you minimize the amount that dries on your mixing surface.
Hmm. Looks like the 5"x8" steel shingles I get are galvanized. Maybe they have non-galvanized ones...