With ski touring as your main goal you should focus on the aerobic base work we advocate. If you are packing 30 extra pounds of meat up the hills that is going to seriously impact your ski touring enjoyment. Look at the build of most mountain athletes and you will see slight individuals. We do not advocate hypertrophic (physique or body building) training for athletes. Of course you need to maintain and build enough strength to protect your back.
With my interpretation of your description I would place 80% of all strength focus on the core work. This is what will protect your back better than anything. For 35 years I’ve had severe spondylolisthesis in one of my lumbar vertebra (forget which one). This is the displacement of one vertebra 1/4″ forward causing hyperlordosis and sever strain on the discs above and below. I have to really work on my core strength all the time, really focusing on the Transverse Abdominus. The TA is like a big girdle around your mid section, besides containing your guts it does the lion’s share of core support for all movements. This makes it a top priority for an athlete to strengthen.
With a back like your you should probably avoid heavy lifts like squat and deadlift and any overheard lifts.
Being an uphill athlete means having a high power relative to weight ratio. Being a tactical athlete can mean just having absolute power.
I hope this helps.