Final update just in case somebody is looking for info in the future.
I have still hard nothing from MPPSolar re the TCP gadget interface. As mentioned earlier, I went back to seeing if my IP remote USB server could be made to work reliably. I uninstalled all the relevant driver and software for both the Sedna and Welland models from my desktopand reinstalled the latest drivers for both:
Sedna -USBServer_Setup_15_0126_0058.exe
Welland-nh204-USBServer_Setup_10_0917_0048_WHQL.zip
Tried the Sedna and it all worked OK, then tried the Welland NH204 and it also worked OK.
However both still had a reliability issue, apparently lockingup
To cut a long story short, while I had the Welland in use, I decided to wall-mount it, but the homemade ethernet cable connecting it tothe LANswitch in the shedwas too short for the new position, so I replaced it with a longer store-bought ethernet cable. Viola! It has now run perfectly for over three weeks, so I suspect my home built cable was right on the edge of being faulty, perhaps temp changes were sufficient for itto lose continuity. (And that's the reason I alsodon't make humongous DIY powerwalls
If I can stuff up a simple ethernet crimp plug, imagine what I could do with a bunch of energetic 18650's.)
Anyways, all is fine, touch wood, and the PCM60X now workshappily to MPP tracker on my desktop, 80 metres away in a different building,via Ebay serial/USB dongle, Welland USB server toCAT5and powerline ethernet LAN.