I agree it sounds like a bad connection. If you melted it at the case, then that is where you most likely had a loose connection. You really need to crank down hard. I've also seen some fuse connectors that COULD be connected with a screwdriver. You won't get it tight enough without a wrench.
* Almost every amp has on-board fuses. Those fuses are for the amp.
* Your inline fuse needs to be rated higher than your total amp(s) fuse(s).
* Your wiring needs to be capable of more than what the inline fuse will be rated at. You can go as big as you'd like with the wire, and it only takes up a little more physical space, and costs a little more to buy.
* Your inline fuse on the wire is supposed to be as close to, or at the battery to protect the wire, (any length not fused from battery to fuse is prone to melting and causing a catastrophic meltdown).
*The inline fuse on the wire, needs to be less than what the wire is capable of handling or else it is pointless. The fuse is there to INTENTIONALLY be the weak point in the circuit. IF it's going to fail, then you would like it to fail where it is protected and can be the easiest fix.