Detail the planters like this:

Set the rebar, waterproof with American Hydrotech MM6125FR, add protection layer, pour the curbs (knockouts where needed for drainage), then bolt the planters down.  No complicated flashing.  No penetration of the waterproofing.  Simple, long-term waterproofing.

Utilities are best run through the concrete curbs as seen below.  Drains can be set in these areas and knockouts or PVC half pipes can be cast into the curb to allow water movement and drainage.

Simplify the design and detailing for efficient and effective long-term watertight integrity.