As mentioned already, the idea is to propose the easiest DIY approach. First option, the most often found, is to build a glass or acrylic tank, with panels silicon glued or polymer mold. Instead, the idea here is to use plastic boxes. Special ones, because I already tried with more basic model that you think may do the job and can find in DIY stores, but no, I advise you instead to directly consider best option, not specially more expensive but much stronger (and even recycled plastic).
(Price indication in Germay in 2022.Q4)
Wham Bam Heavy Duty Recycled Box What More UK manufacturer Iwonatec online shop
62L with lid - 59,5 x 40 x 37 cm - main SUMP -> 20€
24L with lid - 38,5 x 29 x 31,5 cm - roll paper and moving bed modules -> 10€
6.5L with lid - 29 x 19 x 21,5 cm - waster paper and motor holder -> 7€
In addition, internal module for fluidized moving bed will be made with more basic and thinner ORTHEX SmartStore Classic 13 Box Iwonatec online shop
15 Liter - 28 x 28 x 32 cm - moving bed module -> 8€
Boxes Wham Bam Heavy Duty
Available on long term, lot of sizing and even recycle plastic