Couple of thoughts on using foam / Polyurethane glue:
To provide bonding to the glass wall you can do a couple of things.
1) Mix a few drops of Black acrylic paint (Art supply, not exterior paint) to Gorilla Glue / polyurethane glue to make the color black. The acrylic (water base paint) actually speeds the curing / expanding of the glue. The black also makes any exposed / visible areas more visually more appealing.
2) If the glass is not safety glass you can sand / etch the glass to give it a bit of tooth, so that the glue will bond better. On larger tanks some of the glass may be safety glass and you do not want to sand it because that can cause the glass to shatter. Clean the glass surface well to remove any glass dust. Clean it even if you don't sand it to get the best bonding possible.
Spread the glue mixture on the glass area to be covered / bonded to.
Push the egg create method and embed it into the curing / expanding glue. Hold it down as it expands into the egg create unit it is at least partially cured.
2) Spritz the egg create very lightly with a very fine mist of water.
3) Spray black expanding foam into egg create. This can be done while the expanding glue is still setting. You can let the layer fo foam cure and then add another layer but there are ways to do heavier deeper layers and still get complete curing ...
Foam and polyurethane glues actually requires moisture to cure. Typically they get that moisture from the air. One of the problems with spray foam is that with the glass wall at the rear, if you spray too thick of a layer with foam, the outer layer of foam can cure and thus encapsulate the uncured foam beneath because it will keep moisture from reaching the uncured foam underneath before everything can set up. This can create gooy pockets of uncured foam.
Here is a method for doing large deep foam projects in one shot without ending up with pockets of uncured foam.
How to foam larger layers of Expanding foam in ONE shot.
4 a) Install the foam in thinner layers lightly misting with water in between each layer of foam. This can be done while the foam is still uncured and is still expanding. Doing this will allow you apply another layer right on top of the expanding uncured foam. Alternating foam / mist / foam / mist / etc. will eliminate goopy pockets of uncured foam and will allow the layers of foam to expand together and each layer of foam can fully and properly cure.
4 b) You could not use a spray mister, but could inject humidity into the enclosure by using an ultrasonic vapor machine like we use for fogging tanks. This will lay down a very thin layer of moisture. This cloud eliminates any possibility of applying to much water. Then spray on the next layer of foam.
4 c) Before you foam anything, lay out strips of damped newspaper. After your 1st layer of foam, add strips of moist newspaper onto the expanding foam before adding the next layer of foam. Do not cover the entire layer with damp newspaper, just add periodic strips across the foam. Add the next layer of foam.
Adding moisture between the layers also speeds the reaction along. No longer do you need to wait days hoping everything cures.
Doing these things will allow the center to cure at the same time and rate as the exterior allowing you to build a very large and deep project in one shot with foam. The only thing you might find is that the foam may be a bit denser / stronger because the top layers may cause some compression of the lower levels of foam.
If you ever do get an area of uncured goopy pocket of foam there is no need to pull out the upper layers of cured foam to get to the lower uncured section. Just poke some holes through the layers to get down into the gooy pocket, inject a small amount of water into the pocket. That will reinvigorate the curing process.
(By getting moisture between the layers of foam you can even use expanding foam within fully an enclosed molds to create a foam copy of a mold. (make sure you use a proper foam release if you try this.)
I have been using colored foam for years. Something I don't understand is why more folks are not using the black spray foams that are available. They are the same material that make up Great Stuff, only are black in color which makes them much easier to cover and make look natural. The costs now are about the same as a can of the yellow / tan great stuff people have been using for years.