I'd strictly perform FF1 on the entire postal code. That means converting the code to a number in the range $\big[0,26\cdot10\cdot26\cdot10\cdot26\cdot10\big)$ and then encrypting, decrypting and getting it back. This is relatively simple base conversion so it should be easily done using division and remainder math.

Obviously, otherwise you may leak repetition of parts of the input. E.g. you may also have Sneezy's postal code, $\mathtt{H0H\space1H0}$ in there ($\mathtt{H1H\space0H1}$ was already taken by the evil witch). Now you can see that $\mathtt{H0H}$ repeats, so anybody knowing Sneezy's code will also indicate the first part of Santa's code; not good. With many known postal codes - many of which may already be known - this means that it will become easy to quickly guess all the postal codes. If one is relatively unique then it clearly indicates a rather sparsely populated part of the country.

Other schemes may have similar issues, it kind of depends on how the postal codes are generated.

I'd strictly perform FF1 on the entire postal code. That means converting the code to a number in the range $\big[0,26\cdot10\cdot26\cdot10\cdot26\cdot10\big)$ and then encrypting, decrypting and getting it back. This is relatively simple base conversion so it should be easily done using division and remainder math.

Obviously, otherwise you may leak repetition of parts of the input. For instance, if we encrypt the first and second part separately, you may also have Sneezy's postal code, $\mathtt{H0H\space1H0}$ in there ($\mathtt{H1H\space0H1}$ was already taken by the evil witch). Now you can see that $\mathtt{H0H}$ repeats, so anybody knowing Sneezy's code will also indicate the first part of Santa's code; not good. 

With many known postal codes - many of which may already be known - this means that it will become easy to quickly guess all the postal codes. If one is relatively unique then it clearly indicates a rather sparsely populated part of the country.

Other schemes - like the one you are proposing - may have similar issues, it kind of depends on how the postal codes are generated. By converting the entire postal code to a number issues such as these can be avoided.

I'd strictly perform FF1 on the entire postal code. Obviously, otherwise you may leak repetition of parts of the input. E.g. you may also have Sneezy's postal code, $\mathtt{H0H\space1H0}$ in there ($\mathtt{H1H\space0H1}$ was already taken by the evil witch). Now you can see that $\mathtt{H0H}$ repeats, so anybody knowing Sneezy's code will also indicate the first part of Santa's code; not good. With many known postal codes - many of which may already be known - this means that it will become easy to quickly guess all the postal codes. If one is relatively unique then it clearly indicates a rather sparsely populated part of the country.

That means converting the code to a number in the rage $\big[0,26\cdot10\cdot26\cdot10\cdot26\cdot10\big)$ and then encrypting, decrypting and getting it back. This is relatively simple base conversion so it should be easily done using division and remainder math.

I'd strictly perform FF1 on the entire postal code. That means converting the code to a number in the range $\big[0,26\cdot10\cdot26\cdot10\cdot26\cdot10\big)$ and then encrypting, decrypting and getting it back. This is relatively simple base conversion so it should be easily done using division and remainder math.

Obviously, otherwise you may leak repetition of parts of the input. E.g. you may also have Sneezy's postal code, $\mathtt{H0H\space1H0}$ in there ($\mathtt{H1H\space0H1}$ was already taken by the evil witch). Now you can see that $\mathtt{H0H}$ repeats, so anybody knowing Sneezy's code will also indicate the first part of Santa's code; not good. With many known postal codes - many of which may already be known - this means that it will become easy to quickly guess all the postal codes. If one is relatively unique then it clearly indicates a rather sparsely populated part of the country.

Other schemes may have similar issues, it kind of depends on how the postal codes are generated.