Pipework modeling is of different approach since auto spool system generated (Pipe Spool) is already acceptable and detailed items e.g. MTO, spool pieces & others are shown on the piping isometrics but in cable trays I'm not sure if you do also this kind of isometric drawings.
Cable trays / ladders also does auto spool the same as with the pipework but the you need to FILL the tray / ladder according their specs for the actual graphical representations and for MTO. Moreover if you want to create a much more automated macro for this, you need to start to read and understand the pml macros in order to do your own customization. Try to look for this macro files in your PDMSUI / PMLUI to have a good idea to start. FFILL IFILL FFILL MFILLB MFILLCC MFILLSC MFILLCE
You can get the location of your PDMSUI / PMLUI, type in the command line; Q EVAR PDMSUI
Q EVAR PMLUI
Search the files on the given directory in your command window. Files are located on this directory as for my case and may vary depending on the version you're using. C:\AVEVA\Plant\PDMS12.1.SP4\PDMSUI\des\cabl
C:\Program Files (x86)\AVEVA\Everything3D2.XX\PMLUI\des\cabl