Just be aggressive. Mortar pit has a generous minimum range and bofors takes a fair amount of time to build. Just keep your map presence and don't let him get too entrenched easily. If he does start to get entrenched, cap around him and focus on tech. Brummbar or Jp4 will chew up emplacements very quickly.
The only thing you really have to worry about is a 17lber but in my experience most players don't build them in favour of an AT gun or two and more bofors/mortars.
"cap around him" this doesn't work on 90% of maps. Mortar/Bofors barrage usually still in range.
"Dont let him get to entrenched easily". Once the first bofors is up there is nothing you can do to stop it multiplying since you wont have the tools yet.
"Brummbar or Jp4 will chew up emplacements very quickly." I don't know what level you play at, but I'd advise you to play a top 50 brit player who uses this strat and you will quickly find out why they don't work.