I just wanted to make sure you knew that there are big fires burning in Northern Calif. I went out to Shasta Dam overlook and couldn't even see the dam from the observation pullout.
I'm sure the houseboat will be great. I find these situations are a lot better once you are in the situation. I would recommend bringing indoor activities for your son. The air quality was in the unhealthy range and with the current high heat (it was 113 yesterday) I'm sure it will get worse. Also the Lake is REALLY low already.
On a side note - I would call the houseboat rental and see if you can get a discount or some free gas. My cousin says that they were offering a week free next year if you rent a week this year or a free jet ski to use.
Last year, I kept my 18 month old in one of those swim suits with the built in life vest. You can also look for the Safety Turtle bracelet that screams if your child falls in the water. It called Safety Turtle (but it's $267). Just an extra precaution and peace of mind.
Have a great summer and it will be fun. I know it!