What was 2004’s hottest securitization asset? A strong case can be made for the subprime mortgage sector, where issuance volume soared to record heights amid red-hot demand from investors. According to data compiled by Inside MBS & ABS, $401.46 billion in securities backed by subprime first and second mortgages and re-performing loans were issued last year. That performance, a 98.2 percent jump from 2003, marked the best year ever for the market. …