First how I created moving bomb area:
I created a simple box, used func_tanktrain and created two path_track's. Then I created a button I can set the func_tanktrain moving (only one place). Then I just created normal func_bomb_target above the moving box (Name: train1) and set Parent as "train1". It worked first round but at the second round it deleted bombzone. After map restart it works again at first round.

This could be used for example using button that brings bombplace in specific place.