If you are looking for the function of the OD relay (boots up in energized mode, alternate action from a button) then use it, but add a standard mechanical relay to handle the load of the fog lamps. As Volvodad points out, the automatic OD's electronic relay has a very thin circuit board trace in its contact path, sometimes made known to those who try to cure a frayed solenoid wire with a bigger fuse. The relay itself (inside) is the same as any other 30A automotive relay.
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Art Benstein near Baltimore

If speed counted, rabbits would rule the world.