Yes, the 30 amp fuse in the green holder is the main fuse for the battery connection (if you have a power jack you should have another, either similar or identical, for it).
Have you checked the battery disconnect switch? You don't mention the year of your trailer, but, the majority of FunFinders made after mid-'08 and '09 models have them. If that switch got turned "off", either accidentally or intentionally, then you also won't have 12v power... The disconnect is usually, on FunFinders, a silver pull knob (if you are old enough to remember manual chokes it looks like one of those). Pull it out to connect the battery's output to the trailer and push it in to "disconnect" the battery. Don't know the location, but, most FunFinders usually have them located inside the forward pass through or inside the trailer in the main switch panel where the switches for the lights, pump, etc. is located.