There are a number of phot0s on this site of Cobra's with batteries in the trunk area. I moved mine to the trunk about two years ago because of the under hood heat. The main concerns are getting the battery mounted safely so its not going to hop around and that your positive cable is of sufficent diameter, usually a #1 or # 2 cable, don't go cheap, use the biggest cable you can afford/find. I also went with a sealed battery, in my case Delkor made locally but an Optima is the one of the best. You don't have to keep checking the water level with these. There are some pretty fancy billet holders made for them too, see
www.billetspecialties.com for a nice one, starts around $79 . I bought a Kit from Summitt, came with the wires, battery terminals and marine case, was on a one day sale, think they run about $50 usually. So far, no problem as long as you have a good chassis ground and watch where you route the cables to the front. Avoid heat and sharp edges, don't let it flop around. SAme with the battery, must be secure but not so tight you crack the edges. I also put a cut off switch in the ground line to the chassis as a extra thieft stopper. I have also seen guys mounting the battery behind the driver's seat, infront of roll bars, sealed battery only. Good luck