Haskell's On30 RTR model has room for a decoder in the smokebox, and a speaker in the coal bunker. If you're prepared to rework the model, options for the speaker(s) may include the water tanks (with weights removed) or in the firebox. To access the 8 pin plug, remove the small hatch cover on the underside of the loco, near the 2nd driver. Once removed, use a jeweller's screwdriver to remove the screw inside the hatch and once removed, the boiler top is free.
The 8pin socket PCB is located in the smokebox and needs to be extracted in order to plug the decoder in. Once the PCB is extracted, plug the decoder in, being careful not to pull on the red and black pickup wires. If they break (which they can quite easily), the loco must be completely disassembled in order to resolder the wires to the pickups (see picture at bottom of page!).
Insert the stay alive into the centre steam dome and fit the brass weights in the other domes if desired.
Next, solder the decoder's brown speaker wires to the PCB that the decoder plugs into, where the purple wires connect. These purple wires run from the PCB to a small PCB in the coal bunker.
Remove the coal bunker top (it slides vertically up and out), and pull the small PCB through and remove it from the purple wires in the bunker. Then solder the speaker to the two purple wires. Place the speaker in the coal bunker and refit the bunker floor as well as boiler top into position. When positioning and fixing the boiler top in place, pay attention to keeping wires away from the drive mechanism and from the join in the boiler (crushed wire alert!).