Fastening Realtrax to benchwork

Some people use zip ties, in this case the real small ones would likely work.   This way the track can be held snugly to the sub-roadbed and foam.     I think your idea of using the 2" foam is right on, it will allow you to make ditches and streams by removing material, which gives you so much flexibility, to not have to worry about gradients.    A lot of model railroaders don't realize that, and then scratch their heads later, and wish they had.   You may find that you don't even need the plywood everywhere.    There are also things you can use between the foam, and the track bed.    Others have tried various things with varying results, in order to keep the noise level down when running the trains.

I suggest that you do a search (up above) of the website and read what others have done, for this, there will be a lot of info presented.    Use key words like zip ties, phrases like securing track to roadbed, etc.   It will be most helpful, but I definitely agree with the 2" foam.

The screw is a #4 x 3/4" panhead Philips machine screws. that fits in the hole.

The small cable tie head hides in the bevel and a second is attached underneath to secure it.

After working with over 200' of RealTrax, it needs more than one on every track in a few places. Some of the joints won't stay tightly together causing one to use  a fastener on both sides of a joint. Some fit better and you can use one. You'll get a feel for it when it's assembled.

Longs screws in the foam just won't hold it in my opinion. I was on wood, so I used screws.

I really haven't heard of a better idea than the cable ties on foam.

More work, but cut out the sub-road and just use the foam between. L-girder method for the benchwork with 1" risers + 1/2" ply for level to the foam and higher\lower for terrain changes. The height of the railhead and track roadbed will level it to just above 2". Confirm the height on your build.