If you enhance the SAP TM collaboration portal with customer extension fields, the following SAP Note might be interesting for you:
2238064 – Collaboration Portal: BAdI /SCMTMS/BADI_GW_CUST_ENH doesn’t contain entity data
This change introduces the new parameter IT_ENTITY_DATA for method MAP_DATA_TO_PROPERTIES for BAdI /SCMTMS/BADIGW_CUST_ENH. This table contains all data which was retrieved to the enhanced Gateway service entity, so that you don’t have to retrieve some data again. As a result, your Gateway service extension should become faster.