I'm preparing supplies to foam in a new gas tank. It appears rigid closed cell foam blocks were used as dams on each side of the lower portion of the previous tank, creating an open channel for drainage to the bilge. Is pourable polyurethane foam compatible with XPS (extruded polystyrene) like Foamular? Or do I need some special rigid foam to recreate the channel? I really don't want a hot chemical slurry when I start pouring the urethane foam.