Thanks for the advice on the seams. I went ahead and spent the money for the fleece tape as this rig has square corners (they hadn't figured out round side transitions in 1995) and several metal flashings over the roof angle joints (where it pitches up to the bathroom/bedroom) and I don't want that metal cutting through the new membrane.
The front section of pressed board will be replaced with quality plywood (same thickness). The weight difference in that one section won't be significant but the added strength will be beneficial.
The old membrane was tucked under both front and rear caps and the instructions that came with the Dicor membrane says to tuck the front but overlap the rear cap. Probably an airflow thing, don't want headwinds getting under the membrane in front or under the cap in back. The old membrane had ZERO butyl tape between it and the caps which was a contributing factor to allowing water in under the end caps. Once I pulled the trim screws, the old membrane pulled easily out from under the caps.
The other major contributing factor was the application of "RV caulk" by both previous owners and this uneducated one last year. DO NOT USE - EVER - "RV caulk" commonly sold at places like Camping World for your roof repair applications! NEVER EVER!
The materials in the roofing membrane will not adhere to the RV caulk and all you are doing is hiding the problem, not fixing it. Sahara RV (Las Vegas) who sold me the RV should have known this roof was going to have a near future problem, but they sell used RV's "as is" and if the buyer doesn't have the knowledge to know what he or she is looking at when they check out RV's, this is the result 2.5 years later. I got up the ladder and looked at the roof before I bought it and "it looked OK to me" ....
Ah, the power of knowledge and 20/20 hindsight! My co-pilot says I'll be a pro when I'm done and can do this as side work .... at 57 years old - my knees are telling me "Hell No!" One and done!
The new membrane is going to get butyl tape, Dicor sealant and then for good measure a topping of Eternabond tape over the cap trims as the old trim inserts which are supposed to protect the screws from moisture are in a billion pieces from 17 years of UV rays. I'll just caulk the side trim screws, the side trims will have butyl tape, membrane, butyl tape, trim per Dicor instructions.
I can surely see where all the money is spent on having a professional RV roofing company do the job ... labor, labor, labor! (and screws) I have filled two plastic tumblers with screws thus far and still haven't taken off the upper level vents/skylight. This roof will get all new screws obviously.
Goal is to be done in 8 days. (One week from Saturday). Once the seam seal tape arrives, all materials will be on site and there's no more excuses not to "Git R Done"!