Arch Support & Base Plates.

For smaller arches I use IKEA lamp bases screwed to MDF for extra weight and stability. These bases are included in the arch price and so I do not return to collect. Aluminium rod slots into the vertical poles and is shaped to create an arch.
For extra support I’ll use suction cups on retail shop fronts:

For larger arches I’ll use metal base plates:

These plates weigh 28.5lbs each and when working outside I’ll screw 2 together to provide a really heavy sturdy base at both sides. I then use the aeropole system connected to the bases adding more poles for bigger arches.
The sweet spot for outdoor arches is 5 poles. This delivers the balance of strength & flexibility.