What is the best thing to do with the vils you use to repair trebs when they are idle?

In late imperial war, I always have some vils around my trebs to repair them. Though i wonder if it is worth it from a cost benefit analysis, since the vils are sitting there idle if the trebs are not attacked.

Is there anything creative that im missing that I can use them for while they are there waiting for the treb to get damaged? I thought about:

- Making them chop wood nearby. Though there might be no wood to chop nearby. And the trip to go to the wood and come back, might be too long and then you lose the trebs before you repair them.

- Make them build palisade gates around. Though these can also disturb your formation.

- Make them build a mill and some farms and they work the farms nearby. Though this occupies front line tiles that are necessary to build stuff.

- Place them inside rams, so the rams go faster, and make the rams patrol in front of the trebs and army to soak up arrows.

- Make them build towers. Place the vils inside the towers when idle, so they attack enemies nearby. I think this is the best.