That sounds a little often, but falls in line with a lot of
recommendations. Remember that lot of gensets on boats don't get 100
hours operation in a year! Running yours as much as you plan, you could
probably go longer, but I'd look into bypass filtration to really get
long life out of your oil change. Check out:
http://www.gulfcoastfilters.com/how_...tine_oil_c.htm
or
http://www.amsoil.com/StoreFront/bmk18.aspx

You can basically eliminate oil changes if you use synthetic oil and
bypass filtration. You do have to test it occasionally though, by
sending off a sample for analysis... maybe $20.