I live out of my FWC Fleet with indoor shower sometimes 6 days a week. In the year that I've had it, I've used it 90+ days. I've found the insulation package reallly helps on cold nights. If your fridge runs off propane, you will go through propane faster & will need both tanks for heating & the stove, as well. If your fridge only runs off solar batteries or shore power, the solar is inefficient on rainy or overcast days. You will either need to charge your batteries by running the engine for 1/2 an hour or hooking up to shore power, if you want to run the furnace at night beyond a 3 day stay. A rechargeable camp light & a flashlight are good backups to conserve power.
If you add a 2 or 3" foam topper to the bed, you will need to remove it to clamp down the camper.
I use a collapsible 5 gal water cube from a sporting goods store & a hose for grey water. I found a rechargeable lighter for lighting the stove invaluable. If you have a digital thermostat, carry spare batteries. Camp towels work great for showering. I use a polyester cooling towel for wiping down condensation from the ceiling & open the vents while parked to dry everything out. Make sure you get deodorizer for the port-a-potty, toilet paper & wipes. An Aeropress works great for making coffee. As others have stated, flush the fresh water tanks, before refilling. A collapsible step stool helps in both getting into & out of the camper and climbing up & down from the bed. An outdoor rug will keep the floor clean. If a white fresh water hose, a filter, & water pressure valve are not included, buy them. Don't waste your money on a Good Sam Club membership, unless you're buying a lot of stuff from Camping World. Learn how to operate the water heater & pump. The fridge works fine on a 2 setting in the winter & a 4 setting in the summer.
Most of all, don't sweat the small stuff & enjoy your travels.