You zero with the crosshairs on the target, I use handwarmers, then you continue to zero on the target and move the reticule in to move the POI onto the bullseys, I previously posted in this thread the reticule coordinates for each different RS scope, ie how many MOA the POI is moved when adjusting the internal digital reticule. Once you have the reticule adjusted, you can write down the coordinates and save them in case you ever use it on another rifle and want to move it back, you just enter the correct coordinates for your rifle again.
I have three of these that I use and they are the only waterproof ones that I know of.
In addition the On-Off and Record switches are super simple to operate via tactile touch in the dark, the screen also dims too, it records in 720X480 30fps NTSC and uses a SDHC card for saving the video.
http://www.x20.org/waterproof-dvr-micro-digital-video-recorder
I have four other mini DVRs from LawMate, RageCams, and another off brand and the SPI one is the easiest to use in the dark and takes plenty of abuse in the swamps. i've used them on FLIR T-50, T-60, T-70, RS64-35, and M-18, all work excellent.
If you call them you most likely can get a better price than just ordering online.
There are lots of portable DVRs out there and I have had the best function with this one, I am sure others will chime in on their experience too:
All you do is connect the RCA adapter from the FLIR RS USB video output to the RCA input on the DVR.
You end up with a Microsoft uncompressed AVI file.