There's a couple I follow on instagram thats been living out of their 4th gen for many months traveling through South America so yes it can be done!
For your cross country trip you'll need to decide where you want to go, what you want to see, or just wander but still need to know what kind of roads or obstacles you're ready to tackle and at what difficulty level you'll turn around. For a 50 states tour on the "most efficient way to see all 50 states" you won't need anything except general maintenance. For the TAT, Moab, Rubicon Trail, etc. you'll obviously need more upgrades for clearance, larger tires, protection etc.
When we plan our long trips out we ended up having to make a checklist to ensure we pack everything. We break it down by which tote things go into, and each tote generally has it's own purpose "kitchen/cooking" "dry foods" "first aid/personal items" "tent/base camp setup" then everything else is packed away in it's own specific place somewhere in/on the runner. "recovery/treds/hilift" "cold food/cooler" "water" "comms and nav" "clothes (including 2 rain jackets!)" "dog bag/doubles as hiking pack" "firewood/trail clearing tools" "mechanic tools/battery jumper/aircompressor" covers our basic trips, we never go off the grid for more than a couple days even on two week adventures so we never get too low on fuel, food, water, ice.
For anything further/more remote than that you'll also want to look into spare parts for common failures, extra fuel, extra water, fridge/freezer, more power sources (dual battery/solar/etc.)
Start planning wayyyyyy in advance and don't buy into the "overland" stuff too much. To a minimalist you need almost nothing. Take some short test trips and stay organized, write down what you forgot and what you brought that you wouldn't ever use. Weight starts to get important when fully loaded up.
