I have a suggestion. We still have enough supplies for two bunkers, right?
Here's what we could do.
Make a wall/trench combination thing from the left bunker on the first trench to the left bunker on the second. Build bunkers about 3/4 of the way back on either side. Draw about a third of the men from that third of the trench line to man these, don't put a commissar with the remaining men, draw the rest from the Heavy Weapons and Artillery battalions and put them in the bunkers and side fortification. If the enemy is smart, he'll see the weakness, and attack. If they aren't, that section will fall first anyway. And then it's a killing field as they try to make it to the next trench line under heavy fire, while the fortification lines allow the rest of us to retreat back along it while blasting away at them.
To assist in this, have two of our artillery emplacements(one mortar emplacement and one basilisk emplacement, preferably) pre-aimed at the area, ready to fire on our command. The enemy commander, if any, will underestimate our artillery, and it will make the killing zone even more effective. If there is no enemy commander, it will still make the killing zone more effective.
Oh, and make sure/ask the commissars to only shoot men who run away before we give the order to fall back.
Really wish we had Valkyries and Sentinels. Leman Russes would be even better of course. After all, digging places for them to entrench themselves(with a ramp so they can reverse out and go to the next one, of course) would fit well, and give us some heavy fire power that's more accurate than a Basilisk. Oh well. Things are what they are.
Keep two field medics in each bunker and three in each redoubt for the front line. The last will be with us. Orderlies will be taking wounded back to the med-bunker and assisting Halmin.