bought 8 yr old house with Trex decking & cedar posts/rails/spindles that previous owner painted with latex. Top boards (approx 8 inches wide by 4-5 ft long by 2 inches) had paint flaking off. I sanded smooth, primed with Sherwin Williams A100 and top coated with Duration. Paint bubbled bubbled (air pockets). Stripped again, this time I used exterior spackle and skim coated / sanded in case there was something on the wood ... same story - bubbled worse. So, now I am thinking sand one more time, try exterior KILZ and see if the primer will hold. Duration on spindles/bottom rail looks great. Top board/rail is the issue. I was also thinking about putting some sort of gloss white vinyl cover on the top rail and averting this issue altogether! Can't locate anyone who does this. Any advice??? Thanks!!!