Since PPCs are currently like flinging blue turtles and are a little toasty I went with ER Large Lasers to compliment a Guass rifle. Case to prevent going boom when the gauss does. Enough ammo to last most of the match. The high mounted lasers are great for peaking over hills and are put on the right side so that if you lose one side torso you still have some decent damage output. If you lose both side torsos you still have another large laser to work with. I use Seismic, Radar Deprivation, and ER Large Laser modules. Screenshot of my first match with this exact setup:
That's not really how CASE works. Case prevents ammo/gaussplosion damage from transferring inward on your mech, in this case, from LT to CT. This is unlikely to happen, as the Gauss would first need to destroy your sizeable LT HP pool before it would begin to go to CT. The odds of that are... maybe 5-10%, and there wouldn't be much damage left to transfer most of the time.
If I were you, I'd build it more like *Stripped your weaponless arm's armor to cram more DHS *Used those extra DHS to pad your arm ERLLas from critical hits *30 Gauss is enough to make a big enough difference in most matches *If you don't want to drop it to a 295, you can still use a 300 but it'll cost you some leg/weapon arm armor (and of course all your stripped arm's armor).