Question is, what can I use as a substitute, I have tried truck wheel
cylinder boots, but the carbon in them upsets the apple cart.

Can you use pieces of suitably-large-diameter heatshrink tubing...
pick a piece comfortably larger in diameter than the innards of the
trap, slide it over, and heat it gently with a hairdryer just
sufficiently to shrink it to the necessary size? The safest size to
use would probably start out at roughly 2x the diameter of the trap
guts... it'd be a snug fit when fully shrunk.

Heatshrink tubing is available in multiple colors... I imagine that
some types of the black variety might have some carbon-black in it,
but it's also available in white and other dyed colors which ought to
have pretty good RF properties.

Otherwise, talk to your local general-purpose professional plastics
supplier, and see what kind of tubing they have in stock.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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