Doff,
AGM batteries are fine. They do not have the cold charging issue Lithium Ion batteries have (can't charge if the batteries are below 32 F). There are pros and cons to both kinds so it is important to understand your need as well as how you will use the batteries.
We have two Lifeline GPL-4CT 6 Volt Deep Cycle AGM batteries that are just over 5 years old and which are healthy and are working well. They are heavy though. Lithium would provide the same usable power with 1/2 the weight and about twice the cost.
It is imperative to have a shunt type battery monitor e.g. Victron BVM-712 or equivalent to measure what your actual power consumption is as well as to measure the state of charge of your battery bank. Everything else follows...
We rarely discharge our battery bank below 65% and almost always fully recharge them everyday before discharging again. We monitor with Victron BVM-702 Battery monitor which has a blue tooth dongle (it is an earlier version before the BVM-72 with built in bluetooth came out)
We had a two panel 200 W solar system with Victron 75/15 Solar Controller and last year the system was upgraded to a 360 W panel and a Victron 100/30 Solar Controller. Even in Alaska in September and October last year we had plenty of power everyday to recharge the battery bank. I don't worry much about battery power and recharging anymore.
I strongly recommend putting the largest single solar panel that will fit on the camper. The additional cost is marginal. Price per watt is less on bigger panels. It is also lighter in weight than using multiple panels. If you already have a solar controller capable of handling a 300+ W panel (24 V - 48 V) then getting more solar power by going to a large 360+ W solar panel is cheaper than changing to (or adding more) Lithium Ion batteries.
We camp year around and periodically find ourselves in temperatures around 0 deg. The camper inside gets down around freezing from time to time. With the AGM battery bank there is no issue or concern with cold charging.
I have lithium on our boat and I know that it will never see temps below zero degrees. Weight is not an issue on the boat so I moved the two 100 W panels and the 75/15 Solar Controller onto the boat. They keep the Lithium Battery bank topped off. I installed a Victron BVM-712 on the boat.
Beware of mixing AGM and lithium on a common charging circuit unless you use a DC to DC charger like the Victron Orion. AGM and Lithium batteries have different chemistries and have different charging profiles. If you simply put them both on the same charge circuit it will result in overcharging the AGM and your starter battery (in your scenario) will be degraded and have a shorter life.
If you do not have a smart alternator in your truck you might alternately consider using a Blue Sea ACR near the truck battery and in between the truck and the camper house Lithium battery bank to protect your AGM battery.
Here is a short video reference:
https://www.pysystems.ca/resources/videos/how-to-charge-a-lithium-battery-house-bank-and-an-agm-starter-battery-at-the-same-time/
I hope this is helpful.
Craig