I read the post as meaning that the 5680 elevation gain is the total over three days -- not that much. To me that is a moderate amount of daily gain. My issue with training this close to a trip is that whan I do a
killer" backpack at the beginning of the season, I am stiff an sore for many days. I would not want to "train" this way and then be stiff and sore on my real trip.

I live in a flat environment so my only aerobic workout in the winters is bicycling. We just do not have enough hills to go up uniless I want to go back and forth 100 times on one puny 200-foot hill! Bicycling is a good way to get the aerobic training without stress on joints. Plus it is fun!

I used to go the to the gym and do th stair-master, which worked but was really boring. If you choose something fun you will do it more regularly.