Living in a camper van or motorhome is a cheap and convenient way to see lots of locations. If you are looking to explore in comfort then it is a great option.
I lived in my camper van for 9 months, and loved it. My vehicle was a converted small Mercedes Sprinter which I converted into a camper van. I spent almost all of my time free camping, with occasional visits to camp sites when in built up areas, and also in rural areas to refresh water supplies and empty toilets, etc.
I travelled in France, Belgium, Spain and Portugal from September to June. I had no problems at all. I know free camping in these areas is more difficult during June, July and August as the police do not like too many people taking up car parks when there are lots of visitors to the beaches.
My camper van looked like an ordinary van from the outside, and so did not attract much attention.
But, If I were going to spend a lot of time living in a vehicle I would consider buying a motorhome as these are more comfortable. But a well converted camper van can be just as comfortable.
For a long period of time I would suggest that you have a wash room, with a toilet and perhaps a simple shower. Toilets are easy to empty with occasional visits to campsites, but showers require a lot of water to be carried. You can generally let the waste water just run onto the ground, but you may have to collect the water if you intend to camp on hard surfaces such as car parks.
If you intend to spend time in northern Europe, or anywhere else that is cold uring winter, I would suggest a heating system of some kind. There are special camper van/motorhome heaters that live outside of the vehicle, run on diesel, and pump heat into the vehicle. These take a bit of work to fit and make some noise with their diesel engine. A simpler option is to get a gas heater that sits on top of a gas bottle, but you need to have some sort of ventilation in the vehicle such as an open window, to allow the burnt gases to escape. You should also insulate the vehicle to ensure that the heat stays in and the cold stays out. Also thick curtains that fit the windows well will keep a lot of heat in.
I would consider a high-top vehicle necessary, to allow standing all of the time in the vehicle. During bad weather, which could last several days, you need to be able to stand comfortably and move around.
Having at least a small area where you can walk around is also good for stretching legs. Typical VW layouts, with the seating across the van is not good for living in a van, and is really only meant for weekend use.
Expenses can be kept to a minimum with free camping, limited driving and buy stocking up at supermarkets. LPG is cheaper to buy in large quantities, so having large gas bottles means you can save money there.
Electrical power is also a consideration. A vehicle for living in should have a good 12v electrical circuit. You would need 1 or maybe more leisure batteries. These should be charged when the engine is running, as this is the quickest way to charge them. Also consider solar panels which will provide a small amount of power during daylight hours. If you need lots of power, for a TV or laptop when consider having several leisure batteries. If you will be free camping away from other people you can get a generator to provide 240v electricity. Wind turbines, like those on yachts, can also provide reasonable levels of 12v electricity, but they can be expensive and need to be taken down from the roof every time you drive the vehicle.
You always have your home with you
You don't have to plan your day looking for accommodation, or end your day short because you need to find a hotel.
You always have a form of transport
You don't have to use public transport. You can drive where you want, when you want. If you are exploring a lot of locations you will save lots of time and money by not using public transport. You do not have to get up early, or wait around for a public transport connection or flight. If you do not like somewhere you just dive on. If you do like somewhere you can stay. You can save lots of time this way
You can stay in beautiful locations
Most campsites are situated in lovely locations, and many have great facilities. However, if you are keen to try free camping (wild camping) then you can stay, for free, in many beautiful locations. There are few things better than watching the sun go down at the beach, and then wake up in the same location in the morning. All just by stepping out of your camper van or motorhome.
Ability to carry possessions
With a camper van you can carry much more than if relying on public transport for a trip. This is great if your trip will incorporate sports such as surfing, wind surfing or cycling.
Camper vans and motorhomes are easy to spot and are a target for thieves. If you are careful you can reduce the chances of theft or damage. Stealth campers can help greatly in making your vehicle 'blend in' to the normal traffic.
Initial cost and maintenance costs of the vehicle
Of course you have to purchase or build a camper van or motorhome, and these generally cost a lot of money. However you can trade in your existing vehicle. If you sleep in the camper van you will save accommodation costs and on a long trip this will work out much cheaper than using public transport and hotels. All vehicles need maintaining, and this can be expensive. Careful driving and good maintenance will keep your costs down.
More difficult to drive and park than a car
Camper vans and motorhomes are bigger and generally more difficult to drive than a car. All modern vehicles will have power steering, big mirrors and more expensive models will have reversing sensors or cameras. But the vehicles are large and require a good deal of care. High or wide vehicles will be limited to where they can go. Many car parks now have height restrictions. There is always somewhere else to park, and pop-top models get around this problem.
A problem when visiting islands
If visiting islands for a day or more taking a vehicle is often not an option. Sometimes taking a vehicle on a ferry is expensive, and often not an option. This can be overcome by finding somewhere secure to park the vehicle and then relying on public transport. Secure parking areas are available in a lot of areas. It is worth asking at campsites if they are able to store the vehicle for you during your separation from it. Campsites often store caravans for people.
Toilets and showers
Most camper vans and motorhomes do not have toilets and showers. This is because they take up a lot of room inside the vehicle, toilets can smell and showers require a lot of fresh and waste water be carried. Bigger motorhomes tend to have a toilet and a shower. It is easy to add a portable toilet to a camper van, but storing it is often a problem, and it will almost certainly smell. Most people tend to use campsites at night, which have showers and toilets. It is normally easy to find a toilet in any area where there are people, even at the beach. Cold water showers are available to most popular beaches in Europe. Whilst cold water showers are not ideal they are free. Solar showers are an option, and it is easy to rig up a simple shower for outdoor use with a camper. Most people rely on campsites and beaches though.