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Within my region, TT/RV EDPM roofs last from 10 to 20 years. At 12-15 year mark, their EDPM roof maternal looses their elasticity and its outer top white layer starts showing black patches. At this condition, the EDPM roof material is wearing out. One can see it. And within a few short years, the entire roof material needs to be replaced.
Since OP mentioned his "'83 16' Scottie RV", his roof is probably factory build. And being 20 years old and if EDPM material, its at its EOL (End of Life). To proactively fix before it starts leaking water, one can:
1 - Replace with new EDPM Sheeting. Very Expensive - if one includes glue, EDPM sheeting and some new outer trim. This EDPM replacement cannot be done by most DIY folks. Thus, contracting this depth of work out is the norm.
2 - If exiting EDPM material is still firmly glued to roof's underlying wood, simply apply Liquid Rubber Roof over existing worn out factory EDPM sheet roofing material. Simply clean (power washer), let dry, tape off its edges, lift the AC unit a few inches and apply liquid rubber with brush / roller, let dry, remove edging tape. Simple DIY task that many folks can do themselves. A few folks in my Seasonal site applied liquid Rubber to their 12-15 year old RV and they love its results. No more black streaks either. And best of all, liquid EDPM is fraction of the cost - compared to new EDPM roof sheeting (with its underlying glue).
If one visits You-Tube and searches for EDPM liquid rubber roof (or other liquid rubber roof coatings), you'll find many positive DIY video clips. And, positive feedback under each video clip as well. IMO, liquid rubber on RV roofs works. And, last for 10-20 years. And best of all, much less cost compared to new EDPM roof sheeting.
If one is talking about "roof treatment?" (which is different question), then many folks recommend NO treatment. But, "treat roof?" is a different question than "roof coatings?" on 20 year old RV/TTs.
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