He has a point… if you are carrying the battery primarily for the purpose of jump starting then there are other solutions worth considering that take up a lot less space and weight. The likelihood of experiencing a battery failure is also pretty rare, especially if you maintain the truck well, meaning changing the battery slightly ahead of schedule (3-5 years) to keep it fresh.
If you use the battery for running accessories, then you can consider just building it into the truck similar to a dual battery setup, or make a battery box / portable power pack and make it usable. You could easily make something like a goal zero unit for far less money and even be able to charge off the 4Runners electrical system when its running, just like a dual battery setup.
You can also downsize a project like this into something a bit more manageable depending on your needs. I built a very simple solar generator out of a 30 cal ammo cam. It includes a 17ah sealed lead acid battery, MPPT solar charge controller, USB charging, and 12v outputs to connect gear. I generally use this inside my tent to provide power for charging and lighting… and a 12v heated blanket because glamping.
I have a couple different solar panel I can use with it as well. If its connected in parallel with the trucks electrical system, can be used to charge the main starter battery as well.