You may have an intermittent open ground that is telling the alternator to go to maximum voltage and amperage for very short periods of time. If that's true your vehicle will start frying more expensive stuff in the future. Open grounds sometimes start slow and get worse as you drive around, and never fix themselves.
If you start adding ground straps between stuff like the engine block and chassis, the alternator housing and the engine block, the a/c compressor and the engine block, the engine block and the negative side of the battery and the problem goes away then you have found what's causing your problem, just not where exactly it's happening.
These high voltage/amperage events that do things like fry the fuse block usually start by hitting a circuit like the fuel pump, headlights or the a/c. For some mechanics this kind of stuff is difficult when they usually spend their time changing a timing belt or replacing spark plugs. Fixing an electrical problem like this does not show much for the work involved and sometimes makes billing the customer for the time spent can be an interesting experience. So, instead they start changing parts. That way the customer can see what's going on and the mechanic can at least show that he/she was doing something.
Try the ground straps and test along the way with your handy multi-meter between these devices. Just make sure the ground straps hit clean, bare, just prepared surfaces. Your local boating supply store has really good ground straps and the spray stuff you can use to seal everything after making the connections.