RFC or IDOC

i have to create Shipment Cost Document (vi01).

I have create a ZIDOC with 4 fields only and now have to create ZFM for Process Code.

But these is no BAPI or Standard FM for Shipment cost.

I have to code BDC inside it (ZFM of process code)

But guys since XI is inplace i think RFC is better option.

What are your view guys..

Any idea welcome..