You planning on putting a flat face (facing into trunk space) on the box? If you think you are going to end up with 1 - 1.5 cu ft then you could go ported depending on yr sub choice and a plastic aero port could be fitted to front face.
I've used glass before for the same reasons as you, never managed enough volume for a ported design.
It's be nice to see, most glassed encosures in tunks are for space saving so are sealed and often volume is still on the small side for the sub too.