Hi Sync,
No, cut some foam into a compartment and close the chip & PCB inside. That is good enough for ovenized x-tal oscillators. Use flexible leads into it. Then, mount the little encapsulated assy inside. I'm trying to suggest something that is mostly COTS with minimal messing around for you.
When I am matching pairs of transistors, a foam cap does a wonderful job of keeping the two parts isolated from the outside environment - and that isn't even sealed. The most important thing is to have freedom from air currents, which this idea will give you. As a side benefit, you get a sealed space that can be kept at whatever temperature the heater (or a heater) will be set at. So a quiet voltage reference, coupled with a heater if it doesn't have one, gives you a stable temperature with no air currents to disturb your reference. Some of the better references, like the
LTZ1000 has.
Other references with a heater are the
http://www.linear.com/product/LM129 family and the LM129 family. For your 5V reference, you might have to use a voltage divider or a buffer with gain with the reference.
Some of the temperature compensated references are getting quite good also. If you keep one of those at a set temperature, it would be extremely stable.
So, what are the main reasons why you needed the metal can? I think Linear Technology has made the new products equal or better in performance. Not unless you need the LTZ1000 level of performance, and then you should probably just buy those. Expensive, I know. Just think of us poor Canadians looking at the exchange rate.
-Chris