[Imp]

On entrenching units the other way to do it is set to assault & buy & deploy the units you want entrenched then switch back to meeting.

To sort of fix once its to late as a suggestion I do this for guns armour.
Use the modify unit button.
Reduce the unit size
Adjust the hull armour.
This does depend a bit on the unit & what is likely to attack it.
For a soft unit like this you could give it a low armour rating so RPGs etc could take it down.
Could give it say 2-3 ERA so has a small chance they "miss" anything important.
Tanks you could add say 30+ to the hull armour rating & boost HEAT to invulnerable.
Any unit you do this to needs its speed set to zero if it wasn't already.