Carrying 50% of BW for prolonged periods is not something we are built for. Even pack animals like mules and horses are normally limited to about 15-20% of BW. Just as the horse packers that operate in the winds. They will only put 200ls on a 1000-1500lb animal.
So you are asking a lot of your body.
If you have enough time I’d suggest a conventional strength progression of 8-12 weeks of general exercises that focus on glute/legs. Squats, Deadlift, Straight leg DL, Single leg straight leg DL, Split Squat, Lunges and any others. The move to a Max period (use the max strength protocols discussed in our book) of about 8 weeks focusing on the single leg movements. Then give yourself 8 weeks for an ME period of weighted climbs.