Since you seem determined to take the difficult route, and you seem not to accept my earlier statement that they are not required, let me at least point you in the right direction.
The gateway entry is used to tell a network host where to send all traffic for any destination NOT on the same network - since your DNS-323 is on a "mini-network" with only two hosts, and you have no intention of sharing it with a third host that is not on that network, a gateway entry may not be required.
DNS server entries are used to tell a network host where to send DNS queries in the event that it needs to reach a host using a URL rather than an ip address - since your DNS-323 is on a "mini-network" and you have no intention of sharing it with a third host that is not on that network, a DNS server entry may not be required.
Please note - the use of the word "may" - whilst the DNS-323 will work fine as a NAS without those entries, certain "non-essential" but nice to have features, such as email alerts and ntp won't work without them - however - as my earlier post indicates, even if you add the entries, they will do you no good unless the PC is capable of providing the necessary routing and/or DNS services.
Now - since you didn't believe me the first two times around - I see no reason why you should take my word this time so ....
GOOGLE is your friend.
You can use it to find out for yourself what the gateway & DNS entries are used for.
You can also use it to find who makes dual disk USB-SATA enclosures that support RAID.
By the way - the DNS-323 CAN be used as you are attempting to use yours - it's just so much easier to use it as it was designed.