I used an old thin ply nuc box that was to hand, with inspiration from here:
I made one out of an old pine brood box I had lying around... it worked but the lessons learned:
I bought a large heavy duty rubber type dustbin from Wickes( am I allowed to say that), then drilled a hole in the lid for the steamer hose and a hole the the bottom for the melted wax to run out. All the old frames go inside then the dustbin is stood on some bricks or similar with the hole over a large bowl or bucket to catch the wax & water running out. Cheap & cheerful but works brilliantly.
I used an old redundant brood box, thick ply top and bottom cut to size, hole in the top for the steamer nozzle and a small cut out in the front of the bottom ply board to let the wax out. All the brood jackets stayed in the box so perfect for a first filter... I'm sure there are much better solutions but this worked as a first time experiment for me