How many watts will you be running total, and what year make vehicle?
If the 2400 fits, under the hood is no problem. With the D2400, you should be good for 2500 watts from under the hood. ( installed properly)
But, used as a supplemental battery, it is good for 4000watts. . So, you could just add it in the back. ( if the factory battery and charging system is healthy. . it will help the cause) Everyone has an opinion on this .. but, I would replace the front battery and add what I need in the back.