What kind of trailer do you have? How big is the LiFePO bank? How many watts of solar do you have on top? How much more room do you have on the roof?
You've got a few options:
1. Wire the trailer to trickle charge through your 7-pin instead of an Anderson plug. It'll keep you topped off while driving but wouldn't charge your bank unless it was a really long road trip. How big is your Lithium bank on your trailer? How many Ah?
2. I'm assuming you've got a solar array on the trailer. Might be way less of a PITA to just add a panel on the trailer if you're not able to keep the charge level sufficient.
3. Lithium banks are awesome because you can use a lot more of the available Ahs and they recharge faster than AGM or Flooded banks. You might be trying to solve a problem that isn't real.
4. If you're still struggling to keep up, you can either increase your bank size or get a portable generator.
5. No more cold beer camping.