Thanks, CLB! I was wondering why no one commented.

Magnetizing the bases was pretty simple. The base molded onto the models is pretty think, so I just drilled shallow holes into it and glued magnets into them. I then glued matching magnets under the normal base. I used 2 to 3 pairs of magnets per model, and it holds pretty well. That said, I would probably use bigger magnets under the base if I were going to do it again. I used 1/16" diameter, 1/32" thick magnets for both sides of the pair, but I think I would get a better hold by using a larger magnet under the base where there's room for it.

I'm happy with how the based models turned out. The bases are Desert Yellow, with sand and static grass glued on top around the black base of the model. It looks good both on the tabletop and in Space Hulk, which was what I was going for.