Are you effectively providing a reporting mechanism for you customers to look at their history?
Can you publish SSRS reports securely?
Alternatively you could consider
-an XML report delivered by a secure webservice.
-CSV reports generated by SSIS which could be downloaded via FTP
The question is, how complicated do you want to go and how much time do you want to invest. Personally, I'm an advocate of keeping it simple so I'd go for the SSRS or SSIS solution.