Some of the usual ways of basing are great and don't need going over because there are tons of intructional posts all over the net to accomplish the look you may be looking for. I even admire, especially for 3mm, the simple super glue them down and splash them with green paint for quick easy basing. I wanted to drop a line about what I use for basing that I stumbled upon just by sheer dumb luck.
My first foray into 3mm was ACW. When most of my supplies had arrived and I had finished painting, I could not find my super glue. I was already in the miniature groove so I picked up what was in the drawer and thought I would give it a try to escape a quick trip to the seventh circle of hell (popular shopping mart). The glue was Gorilla Glue. It was the Gf's and I had never used it before. Well the initial learning curve was a little high but it has worked really well after that.
The glue requires you to put a drop of water down to activate the glue. Then the science-magic starts. The glue will activate and bubble up. And by bubble up I mean completely swallow your miniature if you leave it unattended for to long.
What I have found to combat this is I do 5 - 10 at a time and push the bubbles down with a paper clip I have straightened out. The miniature due to its light weight will need to be pushed down a few times. After ten minutes? I have never really timed this out. Just feels like ten minutes or so. After ten minutes you are left with a very textured, paint able hard undestructable earth looking surface. A splash of brown or earth colored paint and you are ready for some very fine flock in the color of your choice.
I cannot say what this would look like for a desert base because I've never tried to make one yet. It might be possible, do some testing if you are interested.
Pros: quick, very hard, textured surface. Nothing will come loose. Could see it for a quick glue and paint base.
No sand to add, once dry add paint and flock n your done.
You can adjust the texture early on in the process and achieve a look you desire. (Later the glue will be to tacky and try to stick to your tool pulling up)
Can leave select bubbles or select height for some minor contouring.
Cons: No rebasing I'm guessing but come one 3mm is really inexspensive any way.
You leave them and you will have a mini swallowed in a hill of very tough glue and no salvaging it that I can tell.
Make sure your surface has something for the glue to grab onto. Although after gluing 350+ minis and homemade trees to pennies, I had only one tree slip off due to me getting lazy probably and not cleaning the penny properly.
As usual YMMV so test it out.