Lenders are working with different structures to both increase the supply of residential mortgage-backed securities and to relieve concerns of investors who fear that all the problems with securitization — brought to light during the financial crisis — haven’t been addressed. Earlier this year, J.P. Morgan Chase & Co. issued securities that included insurance that would protect the investors in the securities, said Sean Dobson, CEO of Amherst Capital Management LLC, an Austin, Texas, alternatives investment manager.