Its getting time to travel for the season so I just now went ahead and did the final ordering.
I ordered 5 new GoodYear LT Cargo G26 225/70/R15 tires to replace the ST-type tires on the TT, and I also ordered the TST507RV 8 sensor TPMS kit for TV+TT.
I've already ordered and received metal valve stems from Grainger, but I won't know until I go to mount the new TT tires if the metal valve stems will work with my TT wheels. I found another post by wmoses (thanks wmoses) in the Tech Corner forum about using fuel line pieces to strengthen standard valve stems in case the metal valve stems won't work with my TT wheels.
It took three visits to the tire store to get the new TV tires balanced properly last Fall and they are finally good now, so I'm thinking I'll probably use the fuel line pieces for the TV valve stems. I ordered the original style sensors (not flow-thru) for the TST507.
This has been quite a learning experience and many thanks to all who responded and helped me figure all this out...
Marty