Stavros,
Cheap, Quick, and VERY, VERY, VERY Dirty..... The Extender and Inverter pictures are not mine, just screen shots from the internet.
Thanks,
Brad

Pros
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A quite Cheap, Quick, and VERY, VERY, VERY Dirty solution
- Can scale this (with much greater cost) up to an Aruba AP w/ Directional Panel Antenna
centered behind each pair of trailers and eliminate the PEs
Highly Portable
Set PE on floor of trailer entry with view down length of trailer and to the Aruba AP
Use of cheap WiFi (3rd Party) extender
Get WiFi service on the dock for other uses too
Cons
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Extenders can usually only extend up to PSK networks
- No consideration of 2FA
No consideration for weather
- Maybe a plastic container with a snap-on lid
Battery life / Run time
- Have spare inverters charging for swapping
Ideas
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- If you can get an AC extension cord to the entry of the trailer, can eliminate the Inverter
- Height of Aruba AP mounting dependent on obstructions on the dock
- With the inverter eliminated (via ext cord power), the extender could be clipped or suction
cuppped to the inside roof of the trailer (just inside of the door)