Thanks, Phil and I'll apologize now for sounding completely ignorant on this.
With my panel in the fish house being Square D/Homeline, I would be replacing the current breaker (30A I believe) with a 4A breaker similar to what you're referencing (Eaton)? And remember the pump and fan are 240v.
And the AGC style glass fuse would be "inline" so to speak to the fan? In other words I'm sending 4A from my panel, to the outlets in the compressor cabinet (one for the compressor, the other for the fan), then the plug/wire which goes to the fan would be intercepted by the Buss Class J you're referring to?
Or could I just wire an inline fuse [holder], similar to what's used in automotive applications at/near the fan?
Again, please forgive my ignorance as the most basic explanation can still be over my head with some of this stuff!