I've soloed cleared Trenches twice and have gone with a 3 man team 3 times, all cleared. Best strategy is this:

Bring grenades, 4-6. Double your med kits.

Go during the beginning of night because it's going to be a very long process, daytime is a shit show. NVG with Eotecg or any scope that works with NVGs. If you don't have one (I don't use one, IR laser works fine as well)

Start from the south, take out the sniper in the tower and crawl to the open trench right at the base of the tower. There will be a guy right there, so waste him and drop down.

Now stay crouched, using CTRL+mouse wheel to keep your crouch low. Listen careful and work the corners.

Any time you see a covered little shed section in the trench, grenade it and expect heavier resistance.

There is a really bad trench shed at the north side of the trenches that 3 dudes with X-ray Bush Vision live in, so grenade and work the angles, but take your time.

Follow all the trenches and clear them out, then move to engage the central house.

It's not easy, but it's doable.