If you have one or more of the expansions that bring additional NPC types into the game, he can also sometimes be found fulfilling one of those roles. But yes, as KRae says, he starts off as a homeless townie in Sunset Valley.
According to Wikia he often joins the professional sports career. So maybe hanging around the stadium as well as the base might help you find him.
His traits of handy, never nude, vegetarian, slob and heavy sleeper don't really suggest any places where he'd necessary be found, nor does his LTW of The Tinkerer.
Most sims tend to turn up to the library or walk around outside the shops in the Sunset Valley CBD, so maybe keep an eye on that area as well.