From Ian:
Quite simple John, wood blocks are the easiest, inside and along the edge of the cabinet you want to attach clean and lightly sand the fibreglass on the inside to remove any contaminated and deglaze, Apply 5 minute epoxy to the area and side of the block contacting the wall and press into place, holding until the epoxy sets. Then you can use screws through the side of the cabinet into the wood block.
You can also just use fibreglass resin and cloth and bond the cabinets directly to the walls (after cleaning surfaces), but then the cabinets cannot be removed.