I'm using a 2" foamboard subroadbed as a foundation to build my layout on. I had to have the crew at Home Depot cut it apart for me so it would fit in the back of my SUV. With a 4x6 layout table, the foamboard is in 3 pieces. How should I repair these seams? I've read where some people have put down a thin layer of plaster, then painted it an earth tone before starting trackwork, which is what I was thinking about doing. Should I lay out my track and carve out any waterways before repairing the seams?