The Battle Born device appears to be only for LI batteries. The Renogy mentioned above has an optional temp sensor for the alternator. My F-350 has a 200 amp alternator, so if I do something like this, it will be a modest charging rate. My trailer has an enclosed underbelly, so running wires back to where my electrical stuff is would be hard. The limiting factor is the size of the wires that used to be connected to the batteries on the a-frame. I'll have to pull up the sizing chart and see how much I can safely run through the wires. Thanks for all of the responses.
BTW, I've only owned my F-350 for about 3 weeks. I traded in the F-150 Ecoboost for it. One of it's batteries died this morning, so I replaced both today. The battery that died was original. It was paired with one about 6 months old. Grrrrr. The newer battery appears to be OK. So, I guess I have an extra. I was going to check them out eventually. Our plan is in the spring, after the wife retires, to hit the road for a few months. Pushing the F-150 at it's limit for that kind of trip wouldn't have been good for it. So we traded it in.