We've had an FC for about 6 years now. We love it. We use normal fitted sheets on our mattresses, but they are a bit big for one of them. We do normally air the bedding each day - undo the sleeping bags we use and put a tin or two under the mattresses.
We don't take the curtains, mattresses, cushions, etc out of the camper during the winter, but we are very careful - we tip the camper up, raising the jockey wheel. We also air the camper as much as possible during the winter. We don't completely unpack it; we just slide out the beds.
You can also leave all your crockery, cutlery, etc in there. We leave the awning in the camper. We are always very careful about making sure everything is completely dry before we pack it away. We do a last camp in September for a weekend. When we come back, within the next week I completely vacuum the camper, clean out the fridge - we put a little pot of bicarbonate of soda in there. I did try leaving the sleeping bags in there for a few weeks during the summer, but they started to smell a bit damp. I had left them in the main body of the camper, not in a cupboard or anything. Before we put it away for the winter, DH drains out all the water from the pipes. We put bubble wrap right underneath the travel cover.
I also leave towels/teatowels in the drawers from year to year. They are always OK. I have to admit I am a bit obsessed with not getting anything damp.
Be careful about the drain in the sink. The first time we went out we drained pasta or something down the sink and did washing-up, etc. Didn't realise that the outlet under the sink had overflowed into the under-sink cupboard. I don't know if it's still a fault, but the way to fix it is to put a penny washer in the drain hole of the sink.
Sorry that the above is a bit of a epic. Hope it helps. If you need anything more specific, please ask again. I hope you love yours as much as we love ours.