The best 3mm scale trenches I’ve seen were top down images of complete trench systems glued to MDF rectangles. No attempt made to sink entrenched troops into the landscape. Simple, basic but effective and practical. Not to mention easy to store!
I don’t know what the dimensions of the MDF was but I’d guess around 100mm by 50mm. There or thereabouts.
Barbed wire was thin fuse wire wrapped around thin transparent plastic tubing to make coiled wire. Two or three rows to a base. The tubing stopped fat fingers crushing the wire. I’d guess these were around 100mm by 20 or 25mm.
A more artistic version of this hastily created daub 🙂
Growing old is mandatory, growing up is entirely optional!