Thanks all.
Iv started this mod without OBSE, so Ill carry on that way for now. Next time maybe...
Yes, I found both pages on the Wiki, but they didn't really help unfortunately, however, I managed to blag my way around the problem with some creative thinking:
The Trader only sells the one item, so rather than have the usual traders chest, list of items for sale etc, etc, I removed the chest entirely (and the custom item I was using to do this) and instead simply added the item as a choice on the NPC's dialog (along with another choice to turn it down).
Setting this choice item to be the 'Goodbye' item automatically closes the NPC dialog window (Saving me from having to press the big X), and in the script result box I added the following
Player.RemoveItem Gold001 16NPCPodTrader.MoveTo PodTradedMarker01Player.MoveTo PCPodTradedMarker01
This left one issue, in the the trader was originally sitting and appeared at the new location in the same position, where he seemed to get stuck until I left the cell and then returned, at which time he would get up from the invisible chair and make his way to where he sits and trades normally.
I got around that by tacking NPCPodTrader.EvaluatePackage on the end of the previous bit of script, so now he appears as he is getting up, and immediately makes his way back again, which is exactly what I wanted him to do.
Many thanks for your efforts everyone.
MVK