[Espeefan]

Hollowed out fuel tanks and cab steps/battery boxes work well for hiding some items, but only the smaller ones. There are quite a few ESCs out there that can fit into a cab step, tool box step, battery box step, or fuel tank. You can also hide a radio receiver inside such items, but to keep a full interior, the bigger stuff, like a sound or light unit would have to go under the hood. If you have a headache rack/drom box, small battery packs can fit inside those as well, but you'll mostly be stuck running a smaller LiPo, or an 2/3A NiMh pack, which is about 1/2 to 1/3 the size of a larger Sub-C NiMh pack. Likewise, a smaller battery like that can also fit under the hood, or between the chassis frame rails. The only problem with an 2/3A NiMh pack is they have reduced capacity. Only about 1600 mili-amps at best. You can buy a 2S LiPo pack the same size, with about 2250 mili-amps, which is a lot better. Trucks like these do not draw a lot of current, so run times will still be decent. In the 20-30 min range.

Some electrical items can be hidden in the cab too. Stick them to the roof, because a big drop visor will hide them from view. Servonaut's speed controllers and sound units are actually pretty large, but thin. They can be hidden out of view that way. Or mount them to the cab floor, and make a false floor to cover them up.

Something else to consider......ditching the Tamiya 3 speed transmission and going with a more compact gear head or spur gear motor will free up a ton space! Yes, you'll give up having three gears, but I've had 3 speed trucks, and never found myself shifting gears that much anyway.