Reporting success.
After a few days break, I decided to return to attempting to compile the driver for this device and have finally achieved it. What follows is partly a memory jogger for me and partly an assist for other TC users.
From the Realtek web site I downloaded the most recent sources I could find:
RTL8192SU_usb_linux_v2.6.0006.20100625.zip.
From the zip file it seems this provides a driver that is suitable for:
rtl8712, rtl8188, rtl8191, and rtl8192SU devices.
Following a suggestion on #tinycorelinux (thanks jls_legalize) the driver compiled and produced 8712u.ko, which I then compressed to 8712u.ko.gz and turned into an extension:
rtl8712u-2.6.33.3-tinycore.tcz
This places the module in the same path as those in wireless-2.6.33.3-tinycore.tcz and is listed in OnBoot.
The result seems to work well. No dropped connections no crashes. Connection to a router using a 40Mhz frequency, N standard data rate, WPA2 security and 100% signal strength, all give dependable consistent results.