RMAProc and SelectedSerialNumberEntry

I am writing a C# customization that requires the retrieval of the list of serial numbers that was about to be added or/updated to an RMA Line(before RMA line is saved). I need to be able to run some lookups on those serial numbers against reason code on the RMA Detail form.

does anyone know how to link the ttRMAdtl table to the serial number select ttselectserialnumber pre-save?