If your front rest is elevation and windage adjustable a simple rabbit ear rear bag works well for me. If not, I like a rear monopod that adjusts for elevation and windage. I made mine but I think Saber Tatical offer one.
look at "Lab Lifts" on amazon a variety of sizes and build qualities to suit your needs if you are not pressed for time...can get it on alibaba for cheaper ..just takes a few weeks to arrive can look up how to build a rear rests on the forum as well