Thanks for writing in. The M969A2P1 (2330-01-527-4880) is just the regular M969A2 (2330-01-377-9337) with an Add-on Armor (AOA) / Tanker Ballistic Protection System (TBSS) kit installed, and is otherwise identical to that trailer. (See TB 9-2330-336-14 for more background / documentation on this change, as well as a parts listing for the AOA kit.)
To conduct an inventory, you'll need to pull up the component listing for the M969A2, from TM 9-2330-398-10. You can find that TM here: http://www.armyproperty.com/tm/9-2330-398-10
The manual is large (11.2MB) so it will take a while to download.
In addition to the M969A2, this type of change applies to the following other trailers:
M969 (2330-01-050-5634) with AOA kit becomes M969P1 (2330-01-527-4878)
M969A1 (2330-01-155-0048) with AOA kit becomes M969A1P1 (2330-01-527-4879)
Thanks again for writing in!