This is a simple yet effective egg-crate rack holder. They are stackable and have locations for zip ties so you can zip tie the egg-crate to the stand, and the stand to other stands to increase the height.

The egg crate diffuser I have was purchased from Home Depot. It looks like there is a variation in sizes. This egg crate is about 7.5mm tall, and the squares are 15mmx15mm.

Two sizes available, 2" and 1". This should accommodate most peoples needs as they can just continue stacking them higher as needed.

The zip tie holes are 4mm, so if your supports won't come out just use a 4mm drill bit to clear it out.

Print in a material that can withstand saltwater (like PETG).