Your attampt should work.
But dont set a source (i assume nn.nn.nn.nn/22 is your WAN subnet) otherwise you would have to be in this subnet to access the webgui.

Yes I know, I have access enabled for one specific location and if I'm elsewhere I have to use VPN or RDP to another internal server first.

Cheers,

Please try to use punctuation….

This forum provides a search function:
http://forum.pfsense.org/index.php?action=search

in short: create a firewall rule on the WAN-firewallrule-tab with
source any
source-port any
destination WAN-address
destination-port webgui-port

Are you sure that should work? As I recall it I had to put my pfSense LAN address as the target to get it to work (after also having added NAT).

NAT
–---
WAN  TCP  88  192.168.0.1 88

FW rule WAN

TCP  nn.nn.nn.nn/22  *  192.168.0.1  88

Is the above setup not ok? (I mean it works, but that doesn't mean it's "the right way" necessarily).

TIA

This forum provides a search function:
http://forum.pfsense.org/index.php?action=search

in short: create a firewall rule on the WAN-firewallrule-tab with
source any
source-port any
destination WAN-address
destination-port webgui-port