I’ve got a 25A Redarc DC-DC charger in my camper, and I really like it. It has dual inputs, so it can connect to the truck battery and your solar panels, and will prioritize using solar whenever available. It supports lead acid, gel, AGM, and lithium. I currently have a single group 31 AGM battery, but anticipate that someday Li will hit a price point that’s attractive to me.
It also has one benefit that I wasn’t anticipating before installing it, but have come to appreciate. If you have a 3-way fridge in your camper, the DC mode will work noticeably better due to the voltage being maintained about 2.5 volts higher than than it would be with no DC-DC charger.
I like mine enough that I recently noticed that Redarc now has 40 and 50 amp dual input DC-DC chargers, and I will be upgrading mine to a 40 amp.
:):)