The battery holder can be positioned under the chassis if it is not contained within the vacuum formed top. If some care is taken in positioning the motor then sufficient space should be available. The LDR could be contained inside the cover with a small cut-out - allowing some light to enter - and would receive less light if compared to the position shown here
By far the most common error in building the buggy is in accidentally shorting out the tracks with the axle supports. Insulating pads should be added if the support is on the underside (track-side). Check bolts and drill holes for cutting tracks too. Almost tying for top spot on the list of mistakes is the soldering in of components with the wrong polarity. Check and check again!
Pipe-clips are an excellent way of attaching the motor, but again check that the bolt hole does not cut through the PCB tracks. The topic of 'Push Fit' and 'Clearance Fit' is raised in the hole drilling for bearings and for drive pulleys. A micrometer is an essential tool to have around at this stage.
If the variable resistor is positioned as shown here then a 3mm diameter access hole should be drilled before soldering into place. This will allow the sensitivity to the surrounding light to be adjusted once the top has been added.
If the high axle supports are chosen make sure they are sufficiently wide to withstand the strain of the taught rubber drive-band.