I did the same repair on my ute cage last year. Don't bother with the flimsy stuff from the general hardware shops. Go to a trade supplier like RWAP. They manufacture galvanised welded mesh sheets that are actually designed for structural use. Their 50x50mm mesh with 4mm wire is very consistent and holds its shape perfectly when you weld it. Pricing is much better too since they are the manufacturers. You can see all the different sheet sizes they stock here https://rwap.com.au/welded-mesh/ It’ll make your trailer look brand new.