You can get those "T" fuses at local electrical supply. though they may have to special order (took me 3 shops to find it)... Cost is less than you paid though
I blew one a few years ago
Oh the reason the Inverter's panel showed normal voltage et-al when the generator was running is because it was providing the voltage. not the batteries. And it was on the Inverter side of the blown fuse.
Same as my RV when i "DIsconnect" the batteries the indicatgor light still shows them connected... IF I have shore or generator power