For a long time I haven't written anything about solar power in the van, but it's been in use since day one.
Originally we used a portable 50W panel with the caravan, and while it worked well, it did take 3-4 years of camping before it paid for itself. However, it did work for our meagre power requirements.
When we built the van, an external 12v socket was fitted, both to run appliances such as tyre/bed inflators outside, and also to allow the portable solar panel to be used to charge the batteries.
This worked ok, but it did mean putting it out, moving it round, putting it away, all the things we didn't want to be bothered with.
So we mounted it on the roof.
Do you need solar power? If you will always be on sites connected to their electric then it won't be used much and would just add cost and complication. The occasional day or two away without EHU also might not justify solar if you have sufficient battery capacity installed. Possibly a lot longer if you aren't using much electric power with a gas fridge and no TV/games. Solar only works when the sun shines so you will always need to be prepared for when it doesn't anyway.
If you are going to be living in your van parked up in the same place for a lot of time, when there is plenty of sunshine about, then solar will be really useful. It will pay for itself just if your don't want to pay for EHU on sites, though that's getting more difficult.
If you are sure that solar would be an advantage and not too worried about the cost, then there are firms that will sell you a complete kit at the price point you want, it seems a very common setup is two 100W panels, along with all the instructions, as well as telephone help lines should you need them.
If cost is an issue, or you just like to know what's going on, then you will need panels