Dexter;
I generally use 25mm steel fender washers, but after reading about lead rot, I have not only primed them, painted over that with dark burnt umber, but I have also added a strip of thin plasticard to cover the hole and keep the base of the figure away from the metal. As for Gale Force Nine bases. I have recently begun purchasing these to use for all of my 28mm Napoleonic figures (to start with). I now only have to paint the top of the bases using the usual dark burnt umber as the instructions indicate that you should prime the bases before gluing figures directly onto them. I then use loctite super glue and have not had any problems with them. The things I like about these bases is that they are far easier to prep to make ready for the figures, and they rise up just enough so that I can glue laminated paper onto the back of them which has the figure's name or battalion and company name on them.
The guys at Gale Force Nine are great. I deal with Dan (sales representative). I have purchased 30 of the 25 mm round bases; 15 of the 40 mm round bases and 3 of the 40 mm square bases to date, and just finished using up all of my bases on the weekend. When I sent in my most recent order, they responded within 24 hours. I am very happy and the thin black base doesn't really bother me at all. In fact, I think it rather frames the figure quite nicely, and it gives my "four thumbed" friends something to pick the figures up with instead of by the nicely painted figure. Hope this has been helpful.
Regards,
Hitman