Metal close to this.
few years ago I build a 45" x 6' utility trailor, bought the axle fron TSC and got the metal from metals depot, used treated deck boards on the floor put 2 2x6 for the sides it looks good. I'm a mad scientist/cobbler lol
here it is, it's just big enough to haul a 250 4 wheeler or a 38" Bolens riding mower.