I know a guy who keeps a corn snake in a screened porch area in Louisiana. As far as I can tell, he's doing several things wrong, but so far, he's not had any problem. He uses some kind of hot rock for a heat source. I know that practice is completely wrong for snakes, but it's worked for him so far. Even when the temperature drops into the 20's in the winter, the snake can curl in a cave part of the hot rock and survive. I think he just unplugs the hot rock in the summer. We get temperatures in the 90's during the day, but I guess the porch doesn't get much hotter than 90. I'd never keep a snake that way, but it works for him so far.
If you put enough effort into setting up your cage, you could probably make it work, but the expense both in setting up and maintaining the cage would probably be more trouble than you'd want right now. If you built a box around your cage and heated both the box and the cage, you could probably keep temperatures warm enough in the winter. I'd probably buy a nice commercial cage made of plastic and use undertank heating. The cage would need some ventilation on the sides as well as the top. I'd then build a wooden box around the cage with about four to six inches of airspace on the top and sides of the cage. I'd get two or three lamps that are made to be weather resistant and put 150 to 200 watt bulbs in the lamps. I'd have enough room underneath the cage to put the lamps so that they are about eight or ten inches from the cage bottom. I'd put an aquarium in the bottom as well, keep it filled with water, and add an aquarium heater to keep the water as warm as possible (at least 80°F and no more than 100°F). You'd have to experiment with the number of lamps and the wattage of the bulbs to keep the temperature between the wooden box and the cage at around 70 degrees. You'd want the lamps controlled on a simple on/off thermostat to be absolutely sure of this temperature. The point of having the aquarium full of heated water is to keep enough humidity in the box that the air warmed by the lamps doesn't dry your cage too much. For good measure, I'd have the UTH on a separate thermostat from the lights.
If the ideas in the previous paragraph worked, you might be okay for the winter. For the summer, you'd need a different strategy. You'd need to build some kind of shelter so that the sun wouldn't hit your cage directly. If the sun beat on the cage, the heat would be too much. If you could keep the cage shaded, you might be able to keep the cage cool enough with some kind of forced evaporation setup. You'd need to be able to attach an absorbent cloth to the cool side of the cage and maybe to part of the top of the cage. You'd then need some device that would flow enough water onto the cloth to keep the entire cloth damp. To save water and avoid dripping on other parts of the system, I wouldn't want to flow so much water that it was constantly dripping from the bottom of the cloth. However, if you flowed enough water, you might be able to cool the cage that way. For more cooling, you'd need a fan that would blow on the cloth. The heat of evaporation of water is pretty high, so the evaporation that you force by blowing air across the damp cloth should remove a good amount of heat from the cage. Again, I'd want the whole system on a thermostat to turn off the fans and the water at night if they worked too well. You wouldn't want your snake to be too cold in the summer.
I've never tried to do anything this elaborate or heard of anyone else trying it. I think each of these ideas should work. The cost would be pretty big, and the electricity required to run these devices would be an ongoing cost. If San Diego has power shortages the way that the rest of California has sometimes, I wouldn't risk an animal in this setup. Likewise, if water shortages might cause some local government to make you turn off the water, you shouldn't try this setup.
Personally, I'd wait if I were you. I wanted a snake from the time that I was about seven, but I didn't buy my first one until I was 42. Waiting a few more years won't hurt you. I found that earning a couple of engineering degrees and getting a job negates parental objections.
Good luck,
Bill
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It's not how many snakes you have. It's how happy and healthy you can keep them.