I use a mercury manometer for absolute pressure measurements but they are getting hard to find and many companies will not allow their use. I've looked for alternatives and they are there but they are all much more expensive so I haven't had to switch yet. But that is not really your your problem.
The vapor pressure of the resin is not causing bubbles - air is. If you get to very high vacuum you can expand and pop the bubbles but this can take a long time. Bubbles that don't pop will shrink when you release vacuum but will remain as a foam on the surface. Volatiles, like water, acetone or other solvents, will boil under vacuum and expand air bubbles causing them to pop and then the solvent vapor will sweep the air out to the pump. Resin that is boiling will have new bubbles constantly being created and breaking. When you release vacuum, boiling will quickly stop and all bubbles will completely disappear. This is because the bubbbles contain only solvent vapor and no non-condensible air. Volatiles that are below their boiling point will be liquid.
So the trick to degassing resin is to add a few drops of solvent to the surface before pulling vacuum. BYK sell degassing aids. One is simple heptane.
You mention gas trapped in your cured structure so you may be referring to voids which can have many causes. The most common, though, is still trapped air.
