Where your welds are clean you have done well.... the welds hot enough to have penetrated into both sides and you didn't travel to fast that you've under cut
But being a transporter trailer and carrying a bit of weight the last thing you want is it to break, flip it over and do the other side and clean it up as best you can before welding this will help

if you are able to lean it up so the weld puddle when you weld is level not ramping up to the side you'll find it a bit easyer