Looks good so far. Might not need the cross bracing on the inside but on the thinnest section that you have made...that may cause a problem, as that will be the weakest point.
Try and make your cuts on the body reasonably straight otherwise when you go to make the new section you have done you end up with gaps that shouldn't be filled with weld. Make everything as flush as possible.
The one thing I can say with your welds would be to make them overlap more. You don't want to have those small pits in the centre of the welds. I haven't used a pulse MIG before but if it is like doing spot welds on top of each other to get the coin effect then make sure it arcs again before you lose the molten pool from the last weld. This would mean you get a stronger weld.
Otherwise, keep it up dude.
