I’ll be curious how this works out for you. Some years ago I experimented with an external antenna (a cantenna) for a router, and I found that the attenuation of the SMA cable negated any advantage of the cantenna. If I moved the router outside to the 6 inch cantenna wire, it was a significant improvement, but adding a 6 foot wire between the cantenna and the router left me net exactly where I was with the little 2dbi antenna it had.
I had a similar experience on a boat with a highly directional antenna. I had a better experience with a little USB wifi adapter for a PC. Extending the usb cable far enough to have the wifi adapter connected at the 3 inch pigtail of the antenna was better, since the usb cable didn’t have the attenuation problem. I think that is why a lot of the marine wifi setups have POE cables with the router tucked into the antenna base.
Your use case is close to the marine scenario and you might look at those solutions for ideas.