When you're talking about the "roof vent framing", are you talking about the riser on top of the roof that helps the standard roof vent fit onto the TM roof (which is much thinner than most RV's), or about something that is between the aluminum skins?
TM offers a "synthetic wood" roof riser that won't rot out. We recently ordered two of them, replaced one vent and used one of them, and have another to do this summer when the cover comes off (in 1 1/2 weeks
. IMHO it's much better than the metal-wrapped wood riser that came with ours originally.