Nitrobattery
It's pretty simple to do.
1. Remove the tubes first so as to not damage them during the move.
2. Disconnect the fan and the reverb and remove the 4 screws on top, the amp should come right out of the cabinet.
3. Remove the fan from the cabinet and re-mount it to the front of the rack mount kit.
4. Slide in the amp into the rack mount kit and the 4 screws should line up in the same place as they did in the cabinet.
5. That should be it, put it into the rack and put the tubes back in.
The reverb needs to be mounted somewhere in the rack, close enough to re-attach the reverb cables. Unless you do what I did, use a digital reverb instead. You can just leave the reverb pan in the cabinet then.
By the way... I have an old rack mount kit that I used with my Mark III that I'm not using anymore. I put the Mark III into an Imbuya Hardwood cabinet and bought a Triaxis/Simul2:90 to go in the rack.
I'm 99% sure it will fit your Mark IV, make me an offer for it and I can get it out of my garage.
chedgeco... 8)