Can anyone tell me the best way to build trench systems, is there a right or wrong way of doing it.
Any help would be gretly appreciated.
p.s is there certain way to texture them when they have been built.

I'd try a displacement map, pretty stright forward, perhaps a few brushes to make the walls nice..

I Dont think there is a best way, so much as a few ways.

Ive seen some use displacements(terrain) lined with brushes textured with a trench texture

-trench-section models that you line as your trenches



I think the "best" way is to figure out how your maps performance is going to be affected by doing them a certain way, balancing detail and visuals with performance, just like any other section of your map.