The bubbles have to be coming from somewhere.  Have you done the leak drop test properly? perhaps for several hours even?

As suggested degas the resin. ( You can do it in the catch pot with the mould under vacuum sealed by a clamp.  Just increase vac slowly over a couple minutes so it doesnt froth).

Also try throttling the resin feed with a line clamp to slow the infusion down a bit, maybe its just too quick at the moment.

As has been said, it should be possible for you to achieve a pinhole free finish with infusion when done correctly and there is no technical reason i can see that a mostly flat tray should be any different.

With soric you will still have a smooth side like normal.