You can have pretty much everything ever made for Insane working in game at the same time, this way;http://www.insaneheat.com/index.php?topic=6588.0
Here's the method explained.
1. You just need IDFMaker to extract vehicle and map idf files into folders, like you normally do.
2. Make backup copies of the folders to some temp location.
3. Then, you remove everything else
than the .vht files for vehicles and .scn files for maps from the folders (from the Insane/data/ folders, not the temp ones)
4. Pack the idfs with the IDFMaker.
Now your .vht files should be pretty small, 2kb or something.
(Oh and make sure you don't have preview images on in the idf folders, they make pretty sizeable thumbs.db files in the folders)
5. Copy the folders from your backups back to the Insane/data/ folder (DON'T pack the idfs with IDFMaker now)
The game now uses the files from the folders, it only needs the .vht (for vehicles) and .scn (maps) text files to be packed in the idfs.