I think a 4x4 like a landcruiser is too small for what you need. You could fill that just with your own kit. What will you do in the event of biker injury/accident or bike failure?

I have done this twice going to eastern europe so no off roading. First time I used an L200 which was great, second time a crew cab transit. Both times I took a dismantleable bike trailer which was really handy as I had to carry a sick rider while towing his bike and then tow someones bike when it terminally broke down. Whether one of these would work in the desert is a different matter. In the event of serious injury you may need to be able to lie someone down in the vehicle. I didn't have to carry any fuel or camping kit but the truck was full, stuffed full.

I think your light on fuel, especially for the bikes but even then you are overweight for your proposed vehicle, and thats before you add in tools, spares, camping gear etc etc which will very quickly take you well over your 200Kg limit. Are you really only going to be driving 50miles a day, because that will be about your range, if your lucky, in sand fully loaded on 20L of diesel, so your also way under estimating on fuel. You need to allow for getting lost, detours, fuel loss, and garages being shut. A landcruiser will get 10-15mpg in sand. Calculate fuwl useage on that basis, then add 50% safty margin. 140L of diesel doesn't weigh 140Kg and you haven't allowed for container weight, so again, your underestimating your weight there. Ideally, you only want to be running at 50% of max payload off road, 75% max.

Chris Scott used a 101 and it was a bit of a nightmare I believe. Personally I would go for something van size like an Iveco, Mercedes or Reynolds Broughton

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1990 Landcruiser H60. Full rebuild completed 2014