James! I’m so glad you’re giving the BT1D forum a try.
I experience something similar with my 5 mile walks, I can maintain a steady state for 45 minutes and then there will be a drop that requires carbs. My solution at the time was to move the walk to before breakfast so I had only basal insulin on board. Personally I needed a couple of units to deal with the usual morning rise and that supplied my muscles energy needs nicely. Try looking for solutions in your meals and the associated bolus(es) before your workout.
Another thing to try, if it doesn’t ruin your workout plan, if your glucose starts dropping try sprinting for 10-30 seconds. Did you ever see a rise after competitions?
I just started on a pump and tried hiking with a group of T1Ds. My blood sugar was mostly fine, like Joe said, I dialed in a temp basal rate on the drive over, easy peasy. Forgetting sunscreen and too much time in front of the computer were problems the pump couldn’t solve.