If you are re-decalling, it might be worth taking one of the decals in to try to match the blue to the colour of the decal.  The existing blue on the machine may be different due to 18 years of fade and dirt??????  At least that way you should get the backbox close to the decal.

This is what I've also done in the past...I now only use automotive 2k paint for a nice finish, but difficult if you don't have a compressor and all the safety equipment.