Your situation is not entirely unlike one I faced with my own truck camper rig over the last few years, though yours seems to have a lower overall power requirement due to not running a refrigerator. I went with LFP and I'd do it again, given my space constraints and desire to keep it simple. With an upgraded alternator (maybe 165A?) and with the way the GM charging systems work, you should have no problem charging an LFP battery in a 1-2 hour drive, especially if you're not depleting it very far between drives. Of course the addition of 100-200W of solar should easily provide all the power you need, given the loads you're dealing with. More rather than less, depending on space and what you're willing to spend. If you have sun in the area you park your camper, your solar system could negate the need for an installed shore-power charger.
As for cost, there are several good LFP 100AH batteries available for well under $1K, some currently on sale as newer "smart" models are coming on the market. For ultimate simplicity (but requiring your intervention) you could go with a manual battery disconnect or with a simple relay combiner that activates when the truck is running. You definitely want to disconnect an LFP battery from a lead acid starting battery when you're not running the truck or on a shore power charger.
You don't mention what your daily power usage is, but it's possible you might go with a smaller LFP battery, maybe 50AH would suffice, since you can go way below 50% SOC that is typical of AGM or FLA batteries. 50AH can be had around $600 and below. That starts to be not such a pricey and complicated solution compared to some of the options bandied about to solve the charging issues of the other battery technologies...and you get the added benefit of many more deep cycles that LFP provides over Lead Acid batteries.
Note that an LFP battery has a very low internal resistance and to a large extent will suck in whatever power is available in the charging system if the voltage at the battery terminals is high enough. A DC-DC charger can limit the power draw on the alternator and regulate charging of the LFP battery to an appropriate level for longest life (usually .2C-.3C or less...with .2C being 20% of the AH rating of the battery). In my case, the resistance of the wiring between my truck battery/charging system and the LFP battery in my camper was just about ideal to keep the charge rate when I was driving to a short term max of around 38A...and that decreased (and voltage at the battery terminals rose) as the battery charged. Your situation may not work out so fortuitously, but if you have the means to do some measuring and testing, you could likely work out a balance of wire gauge and length that would give you what you need. Or just spend $200 and get a DC-DC charger and be done with it.
Here is a link to my thread and a diagram of my system.
https://www.expeditionportal.com/forum/threads/another-data-point-for-lifepo4.209444/
Cheers
