Thank you for posting this, I had the almost exact same question.
May I ask what you mean exactly about "reporting" and all? I think I'm okay because I went through
Timeshare Store (not just to a family member, etc.) so I have the tax paperwork from them. And by back up documentation I just think you mean proof, like proof of the original sale and then sell price? Sorry for the dumb questions, first time with this experience!