I just started to build my predator and since I have magnetized most of my STC build's I'm posting here how I did it so others my benefit of my little tinkering.
I started by building the turret and cannons.
Next I added 2 medium magnets on the turret front holes as you can see in the next pictures.
Then I clipped the studs and glued some big magnets
After doing so I tested them and worked perfectly, at most I could dremel a better position for the big magnets witch I used because I wanted a really strong adherence in the canon but it is not a must, if you only have medium magnets you can use them, but you must remember that the magnets must be touching each other, so it might be drilling time.
Lastly glued the tops and some magnets on the turret interior, here I must warn you that you must be careful with the placement of the magnets or they will snap to only to one side, it is not difficult only a precise operation where you drop some glue in the rear part of the turret interior and then put the already magnetized piece then drop a magnet on the turret interior then put a non magnet separator between the 2 points and drop the other one and voila It will work wonderfully and with out drilling.
One last word of advice: Check All magnets alignments so you have pieces that snap into place and not pieces that fall apart or resist being next to each other.