This afternoon, I tied the warp thread onto the back apron rod. I decided to use a modification of the overhand knot method described by Deborah Chandler on pp45-46 of “Learning to Weave”. Instead of the simple overhand knot, I tied a slip knot around the warp after passing the threads around the apron rod (see photos below). This allowed me to pull the warp very tightly against the apron rod in order to secure it.
Step 1 – tie an overhand knot around the bundle of warp threads 
Step 2 – pull the knot tight 
Step 3 – pull the warp thread tightly to secure the knot against the apron rod
After all of the warp bundles were tied on, I spread them evenly across the apron rod before turning the loom around in preparation for beaming the warp.
Warp bundles spread evenly across the apron rod