We live aboard in Seabrook, at Seabrook Marina. A 50 foot slip costs us $450 a month plus $75 per month liveaboard
fee. This includes a wifi
connection that, frankly, will not meet the needs of a college student. Electricity depends on the time of the year and how much the air conditioner runs. I would expect your costs to be less since you have a 40 foot boat.
Bathhouses and toilets are ashore and supply never-ending showers.
There are a lot of marinas
on Clear Lake
and most allow liveaboards. Many, like Seabrook, will tack on monthly fee to live aboard. In this area it will not be 50%, as someone else suggested. I would think you will be able to find something for less than $400, including the live aboard fee, with no problem.
Any other cautions or objections by other posters is strictly a matter of discussions between you and your son, your trust in him, and his maturity level.