Using picture frames for bases

[Fullmetaldroogie]

I am looking into painting a desert style Baneblade in the near future. If I use a picture frame for the base how do I go about getting the frame prepared? Do I have to fill it with something? any tips would be appreciated.

[LadyEyes]

I've seen people use foam as a filler for the center to make the "ground". Then it's pretty easy to cut out areas for bases to sit in. (Think pink or blue foam like used in construction.)

[Skrit]

Or you could use fine sand as a base with watered down woodglue as a binder and then add walfiller to create different levels...

[Demi_morgana]

I did such base sevaral times
You can use cork sheets - cheap and very easy to shape, cut etc