Someone showed me , but I'm not exactly sure how it's working.

I've used magnetic pieces in the corners of my foamcore ground tiles for streets of mayhem (used paperlinx but would have preferred kanelinx). The game board (two 4x2 pieces of masonite) is painted with magnetic primer and ground tiles sit on them. This method doesn't allow magnet use for the buildings/props.

I'd like to try a magnetic white board, with the ground tiles backed with magnetic sheet (just card on mag sheet). This would allow walls and props to use magnetic bases (either tape or small magnets).

Some folks have luck with just sticking the walls and props down using small bits of poster tac. I'll probably try this again for a dungeon or caveworks build since it is considerably less expensive than magnets.

I've used pro masterboard on my pubs and caveworks sets and paper linx for my mayhem set. If I have to do it over again I'll use kane linx in the future for all of my sets.

Look at the sticky thread on bobby pins for your clip it walls. They hold better than paperclips and less obtrusive IMO.

Rabbets are used with foamcore to hide the foam edges.

My personal preference is the removable poster tac as I get it for $1. And I think using magnets runs into the hundreds of dollars.

The Removable tac is visible on the clip-it walls, but so are the clips. It can also be used on the props. But its slower to set up.