how many amps are you pulling?? there are several ways to do this. If the devices are electronic, you need "clean" power with direct connections to the battery and a good ground... (the ground is most important) the best way is to always install a relay and an independent wire run from the battery. Then you can use the latch on the relay on any of the connections in the fuse box that have switched power... most all relays come with wiring instructions and you have the piece of mind that you are not stealing some other devices power... let me know how many amps you need and i can provide more ideas... 
