natd when doubled

[Randy Bush]

i am in a hotel which gives me an address from 10/8 on the ether.
i have it plugged into em0 on a -current system.

i have another machine on wireless out the ath0 port which is
configured as 192.168.0.1

my natd.conf is

    dynamic yes
    unregistered_only yes
    interface em0

my ipfw.rules sez

    add divert natd all from 192.168.0.0/24 to any via em0
    add divert natd all from any to 192.168.0.0/24 via ath0

i suspect the latter two are a bit too clever

the two machines can ping eachother over the wireless.  but
nat is just not doing it.

hit me with he clue bat, please

randy