Dancing Hoskuld
Deity
Love it too.
with a trappers post I would even go so far as to make it buildable by hunting units.
Others should need workers though, but cheaper then full scale forts.
If you can externalize that ressource access to make it limited per outpost type.. could you exclude normal forts from ressource access? And make a more expensive "fortified trappers/mining/etc outpost" for those who need both the resource and the fort?
You can make a specific outpost for a specific resource as you can make something enabled by something else. However there is no way to say not available on something. So a fort will be available on everything, you wont be able to limit it to non resource plots. Besides you may build the fort before you discover the tech that revels the resource.