Are you trying to shield E fields (E or H fields? What frequency?
Keep in mind conductive spray is very thin and sparse and limited effectiveness depends heavily on coating thickness and lid seals especially which can act as great antenna. e.g. 1~2mil required or equivalent to 1 oz copper thickness.
A shorted scope probe loop to Spectrum Analyzer works best for cheap near field tests on emissions or a coax with a small loop and keep gap smaller than loop diameter for sensing.
So even if you have a perfect shield on all surfaces the box seams can become strong slot radiators of harmonics, so test it. Often a tinned brass shield on board works better with solder tabs and other times, its not the box that radiates but the long IO cables connected to it. In that case, LPF on interface lines will reduce emissions. THis can be ferrite CM choke and/or feedthru caps in connectors or many other methods.