Howitzer + Panzerwerfer is a bit overkill if you ask me. The best way to use it in my opinion is going for a doctrine like Close Air Support or Command Tank + Pak43, any doctrine without a heavy call in. That way you can savely tech up to T4 without having to save up fuel for a callin tanks. You have the best results with Panzerwerfers wenn driving as close as you can to the designated location and use the barrage for the most effective accuracy.
ill try these out .. but im in love with the arty field officer now, i had never used concentrated barrage ability with panzer werfer around, now i love it, dont know if its an exploit or an intended use to get 2 barrages out in quick succession using concentrated barrage ability + normal barrage.