Terry,
Thank you for the details on your SIPs. I also use coroplast (free to me on Wednesday after the first Tuesday in November of even numbered years
) for my SIP flower boxes and Totes. I use 4" PVC pipe for supports and braided polyester rope for wicks. I do like your coroplast support design.
In your photos, it appears your drainage (overflow) holes are positioned just above the platform. Mine are typically 1/2 inch below the platform.
Thoughts or insight?
Thanks,
Rick