Greg.. this is a case where Joe can ventilate the compartment before start just by manually pushing a switch. It does not get any simpler than that.
I think you and I were thinking along the same lines by using a time delay relay (such as the one on the glow plug circuit) to engage the fan automatically prior to the start of the generator.
The important thing is for the compartment to get ventilated eliminating any chance of vapors or fumes from igniting when the generator starts.