How to make a collecting tray
1) Get a bottle with a screw cap. Preferably the bottle should be like a hip-flask shape (flattish), smooth with no ridges/bumps.
2) Mark out a square/rectangle as big as you can on one of the flat sides. Leave a little margin towards the cap end.
3) Cut the square out and clean any rough/sharp edges.
4) Add glue (superglue/pva) to the object in places where you want the texture to stick and place the object (base) in the tray (careful not to get glue in the tray itself).
5) Sprinkle your texture (salt/sand). Pat down if need be and wait a moment.
6) Dig out your object and tap/brush/shake off any excess texture and then place to one side.
7) Remove trayís cap and pour contents back into its original container.
8) Replace both caps (Tray and the container for the sand).
Now you can base your figures easily and collect all the bits without making a huge mess!
Hope it helps