[panzerkeil]

Is it possible to mod the intervals between vehicles? I find the short length due to lack of realistic interval less realistic than the length caused by the number of vehicles in the column.

Actually this is something you can do yourself easily. But you have to do it for each vehicles independently:

Look for the convoy you want to change in the chief.ini and see waht vehicles make up this convoy. Then lookup these vehicles in the technics.ini.
You will find an entry "best space"
This is the space the vehicle will keep between itself and the vehicle in front. I used the value 32.0 as it seems more natural to me (in real time vehicles don't tend to drive to close together, especially when there is an air threat).
In this way your convoys will be longer without fps loss (especially if you use some of the very high standard custom vehicles skins).

I have made my own custom convoys longer by adding more space + adding 2 or 3 vehicles to each column (+ changing the types ;-)..