In my setting armies are extremely mobile for a multitude of reasons. Pure static defensive lines are just asking to be completely destroyed by smart and devastating weapons, the light particle shielding in the setting is not enough to allow a static target to take repeated fire. The planet's surface is constantly changing, and the local wildlife isn't always friendly. Some are more than capable of ripping through fortifications or destroying a static encampment with relative ease. There are few safe zones, and resources in those areas are already depleted. Resources are scavenged for and processed across the planet. Nearly all the land can be traversed by a vehicle however, some areas are tougher. But it's not going to be mountainous, swampy or environmentally hostile where too routes are commonly blocked off.
Armies in this world operate heavily on the idea of high-low. They are extremely mobile across various terrains with a combination of light and heavy armor along with an attached logistical element. When an advance force scouts out some resources it usually leaves a contingent force to both process and defend the area with resources that just popped up. Usually infantry. The rest of the force is running defensive screens and defending or counterattacking against enemy pushes. Because no one is interested in blowing up the few precious resources that popped up, fighting in the resource areas are more surgical and precise. But the areas surrounding it are a completely different story.
Most APCs like the MRAP or IFVs like the M2/3 Bradley aren't designed to actually let embarked soldiers sleep and live in their vehicles. In my case infantry soldiers need to be able to live and disembark from their vehicles. For tanks, they just need to be able to live. Ignoring fuel, obviously there is a size limit for both a practical and logical consideration. Too big and you're going to be sinking into the ground or suffer in mobility. You're also a large target. Too small and you can't transport many people or sustain combat effectively.
From what I've seen so far, I'm not entirely sure if current designs are suitable for long term use. From both a physical and psychological perspective. MRAPs, LAV25s, and Strikers seem to offer the best designs from reality. But add in some troops, basic gear, backpacks, weapons, personnel affects, and things get crowded and sweaty very fast. Plus, extended sleep is a nightmare especially for anyone in the back.
In this setting simply flying people isn't an option. Expeditions can take days or weeks, so task forces usually travel as a caravan and drive for long distances over long periods of times. There is advanced computing and navigation, but drones work only works in relatively close proximity to the emitter. Long distance drone or even radio control/communications isn't a guarantee.
What would an NBC capable armored personnel carrier or tank look like if it were required to take into extra-long deployment living conditions? What would be the most important features?
These vehicles wouldn't need to carry everything, logistical trucks carry extra food, ammo, water, medicine etc. But ideally soldiers shouldn't have to be going over to the next truck over to grab a water bottle or an MRE all the time. You can completely ignore generator/fuel source for this question. Sleeping and living doesn't have to be a luxury, its fine if people have a cramped bunk or even have to share a bunk. A closed cabin approach is a MUST. The air isn't always healthy enough to breath in without filtering. Sometimes its fatal within seconds to minutes, though harmless through an air filter.