I wanted to report back: I submitted my third Sandbox request (first two were rejected) and received approval 18 hours later. Note that my third application was exactly the same as my first two. Unfortunately, since my flight is in 4 days, I also submitted a Test and Go application and "forgot" to include my trip to Mexico last week. I received approval for my Sandbox application 2 minutes after I submitted my Test and Go application. Hopefully, they will not cancel my approved Sandbox due to this second inconsistent application. Good luck to everyone!!