Getting a bit off topic talking about basements and gardens. (Just doing my job - lol)
In reference to Vampires trying their had at gardening, I built a two-story type of sunroom addition to my house with windows on all of the outside walls and my vampire Sim was OK gardening in that room during the day. He still was sparking and smoking with just a roof over his head, but it stopped after I added the windowed walls. I think I had some problems with plant placement and had to delete one wall so he could plant at night, then replace the wall.
Missa is correct, as long as they are in a vehicle traveling during the day they are OK, Just keep them off the bikes, scooters and motorcycles
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LlamaMama - Other ideas are to have your Vampire Sim learn a musical instrument to play in the subways for tips, or max out on the painting or writing skills. You can make decent money with any of these skills during the day and still enjoy the the clubs and mixology aspects of the game at night.