We need more info in order to be much help:
How do you plan to charge the battries?
Are all the batteries deep cycle?
Are the amp hrs the same in all three batteries?
What size wire connects the batteries over what length run?
In a nutshell your plan will work electrically though how effectively will depend in part on the answers to the above questions. Also, typically the fuse if you use one would be located at the +tive terminal of the last battery in the series hook-up and would be of high amperage rating---like 450 to 500 amps. Its sole purpose is to protect the complete down stream electrical system from catastrophic failure (dead short). Hope this helps, Jack