I originally had the Winnebago valve stem extenders, very light weight plastic/phenolic type tube, and there were no spacer or stabilizing blocks in the outer wheel. Ran that way for eight or nine years, 60K+ miles, without any problems. You may not need the plugs/blocks. When our tires were replaced, longer metal valve stems were installed and were bent to be centered in the hand hole of the outer wheel to make checking air pressure with a straight gauge very easy.
'07 Winnebago Journey 34H, ISB-02, MH2500
Toad - '08 Ford Taurus X
Blue Ox, Aventa
US Gear UBS