We did the same thing with ours. . . it worked great. But AprilsZoo is correct with the trial and error part. Customize it for your vehicle.
However, to solve the "It's too loud" (usually DM & DD), and "I can't hear" (everyone else. . .), we purchased inexpensive external computer speakers (Wal-mart, I think) $15.00 max. But they usually do not work well just plugging them into the headphone jack; not enough volume. So open the TV case, locate the speaker wire, splice into it, (or if you want to get really fancy like I did, go to Radio Shack and get a plug-in and a switch), and taa-daa! Run the speakers to the BACK of the vehicle (with an extension, also at Radio Shack), and everyone is thrilled. The children hear the TV, and DM & DD are happy happy happy with ear drums intact!