Want to build a boat trailer under 750kg what size steel box section?

Question

boat is 14feet empty about 230kg

Answer 1

60x30x3mm.

Answer 2

it depends on how big your boat is ? , for a small speed boat type thing i would not use anything under 3mm  .if using box metal remember to leave the end open for drainage or drill some drainage holes for  when the trailer gets immersed when loading and unloading, i hope this has been some help.  please remember to grease wheel bearings regularly especially on a boat trailer