You don't have to do butt joints with glass. I'm doing a Sea Spirit now and did my butt joints with 1/8 ply (Okume or whatever you're using). Epoxy them down with the grain running long ways end to end on the boat.

What's stiffer, a piece of glass or a piece of plywood? Yes, it will bend fair. Even once the glass is impregnated and hardend, it's not as strong as the ply against the grain. On the outside of the hull my normal glass job just goes over the outside of the joint.

You wet both surfaces, than add some thickened epoxy and I clamp it under a block of wood. I keep my panels from moving with a few push pins in a piece of plywood under it.

The air you're worriedabout is because you're trying to clamp glass with a brick. The glass moves and creates a loose spot. When you glass the hull, that won't happen because you're wetting out with a brush and not clamping and can allow the cloth to spread itself evenly. Also the thicker glass tape thing as the others mentioned.