An important consideration when mounting an access point is that it is easy to access for maintenance. In the event you need to troubleshoot an access point you don’t want to have to pay to rent a bucket truck to reach it, it is best if the access point is relatively easy to take down, with the power injector in a waterproof NEMA enclosure that is accessible standing at the base of the pole.
The best mounting poles are two-stage or multi-stage, allowing the top section to be easily detached and taken down to access the access point. Purchasing a complete telescoping pole system from a vendor is typically between $500 to $1,000, however you can easily create your own for under $100.
Click here for an illustration that shows how to make a DIY two-stage pole, with the top attached with two carriage bolts - by removing one bolt the top can scissor down for easy access. The bottom stage is a 16 ft pressure treated (4"x4") post that is ~ 4 ft. into the ground leaving a 12 ft. exposed post. Then the second stage is a 12 ft. section (optionally you can use a 1.5" galvanized pole) that gets the AP up to 22 feet high
The PoE power injector bricks are 3.25" x 1.75" x 1.125" with a removable power cord. Use a watertight NEMA enclosure with enough room to connect Ethernet cables into the device leaving space to comfortably work in. Good sizes to use are 8" x 8" up to 12" x 12" leaving enough room for a couple of wraps of extra cable, etc. Mount these waterproof boxes holding the power injector in a place that is reachable from a standing position on the ground to make accessing them easy in the event you need to troubleshoot or replace them.
Outdoor Access Points will likely require maintenance over time, so make it easy to access your hardware when the time comes.