Stop over in ours all the time and now use it for our normal camping sleeping accomodation. Every time I do I put the money I’ve saved over Hostels/B&B’s towards something to make it a little comfier.
Wind deflectors so you can open the front windows a little without worrying about the rain to deal with the moisture.
Caravan Bed and cut down an old memory foam mattress. Cut the bed legs down to a height that gets you below the windows but still allows for storage under the bed. Our MPV has a 4ft loadspace so we have 2 side by side for when we both go away. Great for overnight drives on the continent as we take it in turns to get a good sleep. Leave the UK late evening and be ready to ride in the Alps or south of France by mid morning.
Corrugated plastic sheets in black cut with tabs to fit behind trim and a few mm larger than your windows so that they stay in place by friction around the edges to block out the light. One side benefit is that they just look like tinted windows unless you really look close but keep your bike and kit hidden when your in the pub/nip to the shops. Same as the cardboard trick above but more durable and way less obvious from the outside.
We’ve also added leisure battery, split charge, 240v hookup and charge. Cheap electric heater until we can afford an eberspacher. Dome tent awning for living space on multi night stays, plus the usual camping stoves and gear etc Eventula aim is to do a self build camper but this keeps getting delayed as we are more than happy with what we have atm.