I'm having a flash sale of Batbases in various sizes – these are large MDF bases, intended to accommodate entire units of up to two dozen miniatures all together. They can be used with To the Strongest! or other rule systems.
The irregular edges have a naturalistic look, which blends much better with a base cloth than do rectangular bases. The bases are cut from 2mm MDF. Should you wish to magnetize the bases for transport, 3mm diameter magnets (also on sale) can be glued into the holes. If desired, the edges of the bases can be chamfered with a craft knife, and/or sanded, so that they slope down to the table surface. The bases are designed to be stored within a 4-liter Really Useful Box. The image below is of minis mounted on one of the 13cm-wide bases:
All of the on-sale Batbases can be found here.