Paul at EWM link has been developing a line of vacuum-formed terrain items that are inexpensive, nicely done and really useful.
I picked up a pack of the Reinforced Shell Holes.
You get five reinforced shell holes in a pack.
Here is a 1/72 Vietcong on a penny to give you an idea of the size of this 'twin shell-hole'.
I also ordered the big pack of 30 ordinary shell holes (too many to show here!) and received a couple of interesting and useful surprises in my parcel
One of which was an example of a two-man sangar, part of a set yet to be released. Like all the Vac-Formed bits from EWM, this piece is perfectly made for minis based on pennies
Paul at Early War has put tremendous enthusiasm into his Vac-Formed line. It already includes an impressive selection of trench-works. This is definitely something to watch as it continues to evolve.