Congradulation's on the Job and expected new fishermen in your family!
Say with 6 good month's average season (May-Oct) thats $133 a month rent.
You may can get $1000 for the year, But if both you and he are content why push it.
I'm sure if he has a good year You could increase it some next year & still be ahead.
Just be sure he stays on top of mailing the report every month.