I didn't like the aluminum spacers that came with the tank monitor set so I made my own spacer ring to lift a 20 lb North American Propane tank by 10mm for use with Mopeka style sensors.
I don't have a Mopeka “Halo” to compare, but this is similar.
The outside diameter is 210mm (~ 8 3/8").
The slot for the footing ring is 193mm (~7.6") ID, 200mm (~ 7.9") OD.
Updated 2023-06-25:
Version 2 now has drain holes. As originally commented by @wbphelps_250497, I did not think about drainage in the first version. He made a remix with bottom drain holes, but that doesn't work for me as my tanks sit on a flat surface.
My second version has side holes that cut through below the bottom edge of the tank, allowing drainage to both the inside and outside of the ring, as well as cut-outs along the bottom edge of the ring to let water move from inside to out and vice versa if needed to reach the final drain.
To print on an MK3/s/s+, disable skirt and brim to fit the build plate.
I printed mine in PETG and use a 0.8mm nozzle for speed and have had no issues with durability. If printing with the standard 0.4mm nozzle, I suggest 4 or 5 perimeters and possibly increased infill density. With the 0.8, I used 2 perimeters and 20% infill.
The author marked this model as their own original creation.