Our 4Runner has a tape player and CD player, with no input jack. On many trips, it would be nice to just plug in one of the MP3 players, instead of changing CDs. I have used my Goal Zero Rock-out speaker, with mixed results. (It lasted a good long while, but I still had a lot of miles to drive, with no radio reception, when it ran out. It made too much interference to listen and charge at the same time, though I did get a new socket USB outlet that doesn't whine on the radio.) Does anyone have experience with one like this? http://www.amazon.com/Cellet-Cassette-Adapter-Android-Players/dp/B00EP9RW62/ref=sr_1_5?ie=UTF8&qid=1393882476&sr=8-5&keywords=mp3+adapter+for+tape+player There is also this one, but the price seems too good to be worth it: http://www.amazon.com/eForCity-Stereo-Cassette-Adapter-Player/dp/B002SNCOGA/ref=sr_1_2?ie=UTF8&qid=1393882476&sr=8-2&keywords=mp3+adapter+for+tape+player Any other recommendations? DH is not likely to want to replace the whole audio unit, BTW.