Is it possible to put a decoder in 46207 4x4 High Railer?
It should be, but it will be a tight fit. I have not done one, but it appears a tiny decoder like a Digitrax DZ125 would fit. The hardest part will probably be keeping the wiring neat enough that you can still put the unit back together.
Just a reminder that a decoder is not a panacea for poor running. Make sure your high railer is running well before starting to install a decoder.
If there really is not enough room inside the body for a decoder, here are two other thoughts - either build a small trailer for your high railer and hide the decoder in a crate or tool box on the trailer or put the decoder on top of the roof and disguise it with a tarp to look like a roof load.
Jim