Say hello to these shiny 3.4 L reservoirs made from stainless steel. They're completely off the shelf and a set of those GN 1/6-200mm containers with a cut-out lid cost me about 11€. Custom made stainless steel vessels and tanks are going to be way more expensive and I love the fact that these are multi-sourced, clean-cut standard parts. Living in an area where tap water is basically liquid limestone and wanting to add a whiff of fertilizer to the water is bound to spell precipitation and algal troubles, so I'll hope to keep the annoying cleaning part for more important pieces of the kit, i.e. the tubing.
These reservoirs can be inserted into a rectangular mantle with 150 mm x 162 mm outer dimensions. Since I only have 500 mm x 600 mm stock material for the mantle this is going to be rather interesting. I'm aiming for a good fit but will add 45° corner truncations, moving them inwards by 20 mm. I've only done PMMA bending once and found it to be rather much of a pain, what with it bending back again and taking quite a few minutes to freeze in place.
More experimentation will surely be required to get the mantle right.
On youtube different versions of "acrylic bending table" builds are presented that are competing in their ability to set your place on fire.