Hey there dakkanaughts! I finally finished painting my troops and, as promised to myself, bought a predator kit.
Background
Magnets
Notations will be under the image they refer to.
This shows pretty much all the options you have for predator weapons and rhino hatches. I want them all. On the same model.

Magnets.
One on the top of the rear ramp, with its mate just inside the top of the hatchway. One on either side between the interior and exterior body panels.
Another pair of magnets at the back corners allow the top rhino hatch to be magnetized. The door magnets can be hidden better than most, as decorations look better here than elsewhere.
I managed to center the magnets correctly on both the lascannons and the heavy bolters, so they swivel and can be pointed in any direction and left there.
Annihilator pattern
Destructor pattern
Sponson magnets hidden using the sensor/camera things that are supposed to go there anyway. The weapons have a nice big space inside them for the mate.
Next up: magnetizing the turret! Got bored and had to do some painting. This is about my best set of eyes ever, I don't do many bare heads.
Stay tuned, I'll try to post as I do new and interesting things. I forgot to get a shot of the Razorback idea I had, which essential amounts to letting the sponson weapons magnet to each other and placing them over the hole where the turret goes.
Cheers!