How do you get them to the foam, what tools do you use?

A good way to get a nice fair concave is to use a router with a straight bit. set the router for the deepest part of the concave and run it down the center of the board, then reduce the depth setting to make parallel passes on each side of the centerline.

Once you have the depth of the concave marked out in several places, you can use coarse sandpaper or a surform to remove the material in between the grooves you routed out.

or,
put the concave in your rocker table.
clamp the foam to the table
the concave will set when you laminate
either the core or the skin.

-bill