Coach Joe,
I'm with Peter and GRJ as far as the Mianne frame is intended to remain in situ. However, on my smaller 4x8 layout that I moved to the basement, I asked Tim at Mianne to provide caster nuts with 3/4" deep threads to use casters instead of the leveling feet. The idea here is to be able to move the layout to accomodate activity in the area. To strengthen the framework I ordered four more 2' I-beams and six more 4' I-beams to tie together the legs on the bottom. This worked well, and I plan to put a sheet of 3/8 plywood over that level to store the trains. In the pic below, the center lower truss is left out temporarily to add some wiring under the layout. This kit is the same one Tim assembles in his video on the website, I just modified it to my liking.
As to my 8x16 layout in the making upstairs, no cross-bracing is desired, because I need the storage space underneath for tubs, and it won't be moved after the final construction is complete (famous last words).
