Help me make this trailer as light as possible!!!

Need some assistance on rebuilding this trailer I just picked up cheap. I'll be using my small car to pull out and will be picking up escrap with it. Looking to have a max load of 700lbs, so the trailer needs to go on a diet.

It's a 4x6 steel dump bed with a solid axle directly welded to the frame. I have a welder, grinder and most basic hand tools such as socket sets and circular saws.



Im thinking either thinner plywood or possibly steel mesh as the flooring, then tubular iron to make some basic sides. Am I correct in assuming this would shed a lot of weight?

https://imgur.com/a/Ax06l

I would just go the the local boat shop get an old used trailer, down here they are everywhere for around 50 to 100$. Weld or bolt a few thin angle iron for walls, and get a few sheets of tin for the sides and floor should cost around 150$ max and when its seen its last load bring it to the scapyard and build another. Theres a guy by the house did it. Works good and he said it will hold around 600lbs may want to try that. Remember it doesnt have to be conventional or pretty, it just has to work