My Roadster is four years newer than yours but the hood may be the same design ? Mine does biillow slightly with both the hood and sidescreens in place, but only over 60-70mph. At what speed do you encounter the billowing ? The hood fabric should be fairly taut and it sounds as if you have tried many adjustments, have you looked at the "slider" on the frame which gives about a one inch fore-aft adjustment ? (You may need to shorten the short arm of an Allen key to gain access).
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[Linked Image]


Peter
2009 3-litre Roadster "Ivor", royal ivory / green