If you want to make your .TRN files about 2.5 meg smaller then use the flat.asc contained in this zip.

I noticed that MotoXxX41 had been releasing very small Nationals recently.  I remembered that when I created a National that eliminated all the outside terrain it was smaller than 2 meg.  I thought that the national would be the same large size if the terrain was there but flat.  Obviously it isn't.  So I created the flat.asc and tried it out.  What do you know my National was only 2.5 meg.  I will be using flat.asc on all my nationals in the future.

Just put the flat.asc file in the place that you create nationals.  You then need to modify your .TER so that it points to flat.asc.  Every section that contains QuarryF.asc and all the Quarry??.asc's (where ?? is the 8 directions like N, NE, E, SE, S, SW, W, and NW).

AMA_Baatk