The papers/visas are all obtainable on the Moroccan/Mauritanian border, so not necessary to pr-arrange your visa.

There're hundreds of miles of landmine's along the Moroccan and Mauritanian border but a safe passage has been cleared between the border posts. After leaving the Moroccan border you enter "no mans land" which is a couple of kilometers of rough desert before the Mauritanian border post. As soon as you enter "no mans land" you'll get waved down by money changers and guides who will no doubt claim they have the best rates for changing money and that crossing to the Mauritanian border is dangerous without a guide. One chap who crossed 20 minutes in front of us changed some money here and got ripped off! So my advice is ignore all these time wasters. There's loads of traffic using this border and very clear tracks leading across. The plastic fantastic campers cross here with no trouble off-road so any vehicle will get across. The only hazards are some patches of soft sand (easily visible) and stripped out vehicle carcasses (non of which have been destroyed by landmine's).

Entering the Mauritanian border you will be ordered to park so that the inside of your vehicle can be promptly inspected by the boarder guards. I was expecting a search for alcohol, drugs and other illegal items. Instead the guards opened all the cupboards asking if they could have everything they could see. They paid particular attention to the more valuable items such as my guitar and electronic items. This went on for some 15 minutes, they were getting frustrated and I'd had enough. I was adamant that I wouldn't fold and give in to their bullying but enough was enough. I offered them a half empty promotional can of Gillette shaving foam! All but one walked off in disgust and the last guy accepted after a couple more minutes trying to get his hands on something far more valuable. What's my advice for here? It's difficult when so many before have been intimidated by these guys and given them what they wanted. Everyone else I saw at the border gave the guards what they wanted straight away to get rid of them. These guys are government officials getting paid a government salary, they use their authority to intimidate people into giving them gifts. As Mauritania is one of the poorest countries in the world, most of the population are worse off than border officials and could benefit more from these "gifts".
Once your vehicle has been checked you're taken into an office to have some details taken for national security. This is no problem and only your passport is required.

Now you move your vehicle along 50ft to stage two. First you have to go to the immigration window, hand in your passport, where you answer a couple of questions and pay €20 for a 3 day transit visa. Then move along to the customs shed and complete form...

... and pay €10. Then cross the road to a shed to buy insurance and change money.

The whole process took between two and three hours. You are now free to enter Mauritania.

When exciting the country...

Get the customs form stamped at customs, passport to immigration, drive down to the last office (first on the way in) and give passport details. Enter no mans land. This took no longer than 15 minute!