Two normal car batteries connected in series will do the trick. I just installed two Interstate batteries in my truck. They sit in the battery box between the seats just fine. I do not use any type of hold down clamps. I must admit tho, my truck is never used off road, therefore they don't get bounced around. Any decent batteries will work for you. I bought both of mine at the same time, so as to have the same power in each battery.
militarypotts Spec/4 Military Police, Vietnam Era, "Does the noise in my head bother you? Welcome to the Twilight Zone!"