I do not think we need to get into a lot of theory here, It is S and not O gauge, and the SHS S Trax is by nature quiet. For temporary Christmas layouts I use a 1/2" plywood base. properly supported it does not flex at all unlike particle board. On top of that I attach 1/2" white foam insulation using 2 sided carpet tape. No nails into the plywood, no sound transmission and I have a great scenic base for a snow effect. I similarly attach the track with a 3" long piece of 2 sided carpet tape under each track joint. Built this way the layout can be stood vertically on its edge and the foam panel and track will remain attached to the platform.
To get a grade I just use the same 4' long 1/2" foam sheets, calculate the height every 4' and cut sloped pieces off the edge of the foam using a knife and straight edge. cut two pieces to glue together for a 1" width. For curves carefully bend each piece to the right radius then glue them together, clamp the ends and center till dry. then we have a permanent curve with the right % slope. Glue 2" wide pieces of the same foam to the top of the vertical pieces the use the 2 sided tape to hold the track.
I find this cheap, quick and easy. The result is quiet running trains. I do not recommend this for a permanent layout but for a 2 month Holiday layout I think it is fine. I will post a picture.
