Im going to DIY this UQ and I have a sewing machine and some experience(hammock, rayway backpack).I plan to be mostly in warm weather but also very rainy weather. Im trying to go as LIGHT as possible without being cold. I will be hiking on the island of kauai(highest rainfall in the WORLD) where it doesnt get too cold. The average lowest temp is 65. I have used a 55 degree mummy bag with a 1/8 gg thinlight pad and i still got cold. I want to make an underquilt but am confused about certain materials. I just want to know whats best from those with experience.Heres my thoughts so far:

Down UQ w/ M50 shell. very warm, very light, but I will be in rainstorm capital(it rains every day)This seems to be the standard and i already have an old down blanket that i will take the down from. also it gets muggy from the rain so I would like the breathability of down. Just need to know how to keep it dry.
PROs...light, warm, cheap(free down)
Cons...if it gets wet im done

Insultex with M50 shell only on underside. My only concern is some people have had problems with making the UQ properly. It seems to only work if you sew it just right. Not sure if it is as light as down but I heard that it is only very slightly heavier.
PROs...cheap, only need under layer shell, can get wet and dries fast
Cons...VBarrier makes it muggier, I have to buy it, may have problems sewing


Is there any other LIGHT options for a summer UQ. Keep in mind i already have an old down quilt i will use for the down UQ..so free down. Worth it to buy the Insultex?