will help keep it charged if you are driving every few days.

As you mentioned some trailers are also set up so they can recharge the battery from a generator or when connected to power/hookups.

Solar helps too and a simple DIY setup with a 100W panel and a charge controller can be added for under $150 with ebay parts. Surprising efficient for the cost. When I didn’t have a 7 pin connection I used this setup for a week without issue.