Just to offer a different perspective/idea at the risk of being disruptive...
We built a 5x8 portable layout for a local organization. Knowing it would be viewed closely, maybe even jostled as kids crowded around it, we used a looped pile I/O green carpet for the base. Besides looking great, it allowed us to put pads of the hooked Velcro tape on the bottom of layout items such as trees, buildings, people, telephone poles, signs....pretty much anything that might not tolerate an occasional bump of the table without falling over. A light downward press of the item as it was placed ensured a pretty good grip. When it was time to pack up for a move, it all came apart easily, ready for the next time. Also, it gave the participating folks a chance to set up the scenery items differently each time.
Oh yes, we did use felt, too, on the same layout... We bought a couple yards of gray felt, cut it into strips of different lengths to form roadways for the vehicles. The felt also had enough knap to it to 'stick' to the looped pile carpet.
All in all it worked quite well we think.