Before you give up Rob, look at a few You Tube videos and see how it's done. The hardest part for a beginner is cutting the wires off enough so that everything fits in the shell. Once you conquer that part it gets a lot easier. Study your loco before you start and determine where the module would best fit, then where to put the speaker(s), where to run the wires, how to light it, bulbs or LEDs, and how to contain all the parts so they don't get hung up when you put the shell back on.
Some engines you can mount the module above the motor or close to it, some you will have to attach to the inside of the roof, and some you will have to fabricate a mount or mill a weight to get it to fit. But like everything else in model railroading after you've done it for the first time, it gets easier.
Good luck,
Joe