I tried to make this trolley as simple as possible (I have spent far too much time making benches, tool racks etc. etc. instead of getting on and making things!)
I welded as much as possible (rather badly) using a very old 100 amp stick welder. It’s important to strip off all black mill scale with a flap wheel on the cheap steel available from our local guy. It also helps to properly prepare the joint with a bevel or small gap etc. etc. (Still learning!)
The main material for this is 50x50mm tube with wall thickness about 2.6mm (3/32”?) And 18 or 22 mm marine ply. The basic trolley uses just 8 M8 nuts and bolts. The open ends of the tubes make in easy to get the nuts in. The castors are welded on for absolute simplicity.
The bottles are held by bungees but straps would be better.
I varnished the whole lot even over the black mill scale and it seems to have held back the rust even in an unheated workshop.
Later I added some wooden cheeks on the side of the top to give the equipment a bit more security and to provide more tool hanging space.
I also welded a couple of pieces of angle across the trolley and attached some B&Q draw runners and a plastic tray to form a drawer to hold small welding bits and pieces.