How about putting it under the passenger side seat instead?
No room there - I flattened out the floor for my suspension seat and my exhaust is right under it.
Mine is in a boat box in the right rear corner. Held down by a slip type strap. Using a bulkhead connection for the hot cable. The ground is bolted solid to the body. Look up my thread on air conditioning and you might be able to see that there's not enough room to sink the battery into the cowl without having to remove the heater. On that note, they make underdash heaters cheap that might do a better job than the factory heater box.
I'm either going to move my battery higher in it's current mount or move it to the back - I've already for 0GA wire run back there as I thought I was going to put dual batteries back there for onboard air and a welder.
I'm going to be mounting my nitrogen charged bump stops basically on the frame in front of the coil buckets and the battery is in the way. It sits real low in that box I made, I think I can get away with just raising it, as long as I can get the battery in and out of the box that is...
Thanks guys, I really like the look of the battery in the cowl but I'm not ready to ditch my heat yet... and I don't even have doors or a top ;D