You can upload it wherever you like.......you won't get penalised for uploading, say, bank statements into the accommodation section. Do what feels right, just upload enough supporting information without burying them in paperwork. Keep it simple - supply evidence of the genuine relationship/reason to visit, financial adequacy and reasons for the applicant to return to Thailand (so that the ECO can be satisfied that 'on the balance of probability' the applicant is not a flight risk.