[Wiking]

Here's what I did for my last WW2 campaign:

Vehicles that are a total loss (as in the crew is dead and it reports destroyed on the refit/rearm screen) can only be replaced at the end of a "campaign" or "operation." Example: For Fall Weiss, no tanks can be replaced until you're preparing to invade France, and then once again, no tanks can be replaced until that operation concludes. The trouble is once you hit Barbarossa its just one continuous war, so you'd probably have to break it up into periods of operations (For example, maybe break it into June to September and then refit before Operation Typhoon and then no refits until March or April for Case Blue).

For infantry I would only replace damaged squads in a similar fashion, and for man-packed guns like mortars and machineguns I would try to replace destroyed ones immediately, often with an inferior quality captured one to make things more interesting. I figure mortars and machineguns would be reconstituted fairly quickly as their size is small and you can often recover the gun later. Artillery I rarely lost so I had no set system for that admittedly.

To make this more difficult; only repair infantry that are 50% depleted and allow damaged infantry squads to enter the field until they hit 50% loss of manpower. When I used to do that, my infantry losses skyrocketed because suddenly a mortar barrage could kill a 7 man team quite readily, especially since their morale is a bit brittle from losses!