The bases are made from 2-3mm plastic card,texture is nothing more than fine sand,and small.area's of sharp sand or GW's basing sand.
The trick is to use Liquid plastic adhesive,not Pva or super glue.
paint nomore than a 30mm square with plastic glue and cover with fine sand,and repeat until your base is covered.Any gap's in the sand when you've finished with the fine sand,simply drop a little liquid glue in and add a larger sand to the gap.
The whole base will normally dry with in ten minutes.Unlike Pva or Super glue which can require hours to dry when you apply sand to it in large areas(and it gives off some nasty fumes)before you can paint it.
If I'm adding items to a base (chairs tables etc)I pre paint them and super glue them into place and add texture after super glue is dry.
You get very little or no pile up of sand on figures etc when you use liquid plastic glue.
I normally add a pin through the base and into the underside of the model.
Before I attatch the model to the pin and the base I super glue static grass around the pin where it meets the base(it makes a softer looking join and gives additional depth and strength to the joint.)
The reason for the pin is to give an additional ankor point and to take some of the preasure of the wheels.Not where they meet the base but the joint on the body.
I hope this helps.Mark