We have some servers that run in very harsh environments (research vessel) that need to have high-availability.

We have software RAID 1 for some measure of resiliency, along with proper data backups (tapes etc), however we would like to be able to break out a new server and re-image it (including RAID setup) from a known good copy if the hardware completely fails on the production box. Simplicity of the process is a big plus.

I am interested in any advice on the best way to approach this. My current approach (relatively new to Linux administration, totally new to MDADM) is to use DD to take a complete gzipped copy of one of the RAID'ed devices (from a live CD): then reverse the process on the new PC, finally using to re-create and re-build the array.

I'm not sure that this is the best approach, or if it will even work. Any advice would be great.

If your new server is similar hardware (most importantly diskcontroller) you could just clone both disks to the disks in the new server and then put them in to new server at the same position. e.g cloned disk from sata-port0 on original motherboard should go to sata-port0 on new motherboard and the same for sata-port1.
It should boot without having to touch mdadm. You can clone the disks without going through an image file by using something like to save some time. Just make absolutely sure you get the partition-names right to avoid dataloss!!! Check twice before you commit! Believe me, I've been there!