I know where you are coming from Nuttz.
1) Each Barge, Convoy, Train reduces downtime by 30 minutes which means it takes minimum downtime of 30 minutes for 2 hour downtime items ( 3 deliveries ) and 50 minutes for 3 hour downtime items ( 5 deliveries ).
I can see Nuttzs idea but a compromise could be, let the map builder control the resupply time ( how long it takes the barge, train or convoy to reach its destination but it would be the same for all 3 types ).
Note!
Barges and Convoys keep moving unless all are destroyed while Trains can be stopped if you kill the Locomotive, but I guess thats where the Gun cars for the Train come in while the Barges and Convoys don't have protection.
The rivers ( running on land textures ) can not be crossed by Manned Vehicles without dying
( hmmm? this statement is incorrect now??? you can pass over them ) but they can be crossed when the river passes over the water textures ( note the river disappears in that section )
These are just some thing rolling around in my head. I'm with Nuttz HiTech, just thoughts not complaints.
Barges could be used for short distances, Convoys for medium and Trains for Long distances but instead of multiple deliveries have just 1. All could still use the same time but instead of the 10 minutes X 3 trips use 30 minutes X 1 trip.
Barges 30 mph ( 20 mph may be better but distance becomes shorter ) = 15 miles in 30 minutes, worth -90 minutes of downtime.
Convoys 50 mph ( ? 45 mph ? ) = 25 miles in 30 minutes, worth -90 minutes of downtime.
Trains 100 mph = 50 miles in 30 minutes, worth -90 minutes of downtime.
Then I know that this could cause the 50 minutes for the 3 hour downtime items to become 60 minutes for resupply because it would require 2 trips or you could reduce its delivery time to 2 trips of 25 minutes.
Then again you could have trains only resupply the Factories ( country items ) and Barges and Convoys supply the Field items.
hehe just dripple, lost my thoughts

Pokie