It's an SMA connector, and the deck has two layers of fiberglass with balsa core in between, probably all together about 1 inch thick.
What I am looking for is a marine-grade connector that is not to obtrusive when the cable is not connected. This looks good, but it's not coaxial and I wonder if I use this one there might be signal degradation or noise interference because there is no shielding and everything else that makes coaxial so much better suited:
2-Prong Watertight Deck Connection
If you use that one, you can be pretty sure there won't be *any* WIFI signal getting through it. To simplify, RF connectors should look as much as possible like an uninterrupted length of cable.
I too was going to suggest a Type-N barrel, with a gasketed cap similar to the one from the power connector when not in use, but better yet would be a Type-N Bulkhead (or "panel") connector with a flange, sized for the coax run to the router.
Type N Female Panel Mount 4-Hole 1 in. Flange Crimp - ANF-5700
Avoid the solder-type, since at WiFi frequencies you won't be able to make a "clean" constant-impedance RF connection, but a crimp-on - or better yet prefabricated cable/connector assembly - would make for fewer connectors overall, and a smaller hole through the deck. (Notice they mention that "all N connectors are weatherproof" (when mated) as they are internally gasketed - which is why I'd recommend N rather than smaller SMA etc.) Also, I think N gives a decent mounting flange, while most smaller jacks like BNC or TNC mount in a round hole which would require some sort of metal plate which would likely end up being larger than the N flange.
Elsewhere on the L-Com site (no relation to the vendor but I have bought from them several times, always satisfied) they have a "custom cable configurator"
Custom Product Configurator | Custom Cable Assemblies | L-com.com
I did not find an option for the flanged bulkhead connector you would need but a 5-foot run of low-loss cable with an SMA at one end and an N-Female at the other was automatically quoted at $38. I'm sure an email would generate a quote for something similar to a bulkhead jack. If you do, spec the lowest-loss cable you can fit/afford for any run over a few feet.
For what it's worth, I ran Cat-5 to a (formerly Engenius EOC-3220, and since a week ago a Ubiquiti Bullet M2-HP) on the arch. I don't disconnect it (nor does that cable have a waterproof entry as it enters the underside of the arch), but the point is that an external WiFi radio fed by POE Cat5 (Power over Ethernet) or USB avoids RF signal loss in coaxial cable and connectors, which can be considerable. And weatherproof Ethernet and USB connectors are also available.