We fire up the GPS for a trek back to the City of Brotherly Love this week for a fond - but decidedly one-of-a-kind - remembrance of Philadelphia's oddly beloved "octorad"-styled outdoor sports mecca known as Veterans Stadium.   Memoirist, Philly native and actual (Vietnam War) vet Tom Garvey ("The Secret Apartment") joins us to delve into his incredible story of living in a self-fashioned apartment underneath the seats of the old Vet's left-field Section 354 (above the visiting team's baseball bullpen) in the early 1980s:   From the opening chapter of "The Secret Apartment":   "Let's begin an implausible story with a seemingly simple yet complex question: If you were single, never married with no children or dependents, would you, if you had the opportunity, have lived 'on the down low' in a secret apartment in Veterans Stadium?    "In this proposal, we have an off-the-wall South Philly version of 'Phantom of the Opera,' but the larger notion this question begs could easily challenge the inner demons of sports fans anywhere. If you had an opportunity to live in a major sports stadium of a team you grew up loving, what would you have done?   "In my case: I could, so I did."