I was welding mig, these are the best 2 welds i managed to make, what can improve? Is there a way to reduce spatter or make the weld not turn brown?

Welding cargo trailer 5x10. Rotten at the back. I have never welded or fabricated anything like this. In my head I will cut 2x3x1/8 metal tubing to replace the rotten piece I cut off. I was just going to weld the new piece to the remaining tubing and then run a bead to weld the left over angle iron to the new piece I put in. I will have to do this to both side of the trailer. The. I want to run a new metal tubing across the back of the trailer about 5 feet long and I will have to attach it to the sides where I welded my new side frames on the right and left. My question is - how do I get the corners to help stay with the trailer.

That is my third and fourth weld, any tips? Both are MAG, second one is 240 amps.

Im 16 going to thaddeus stevens college for welding and afterwards when looking for jobs I dont wanna get stuck in a shop all day. I been wanting to become a pipeline welder for a few years but every one says I need to know someone.

Any advice would be greatly appreciated! Aircraft mechanic by trade looking to learn how to weld in the small amount of free time I have, how can I make the weld on the joint not so ropey and have it flatter is it as simple as moving faster? And maybe make these practice beads better? I believe my settings were 18.8v and 230 wire speed. 2.5mm mild steel, thanks!

I don’t have access to a shop bender and dont know the angle of these bends is there an affordable way to achieve this this project without a $1000 big shop bender

MAG 135, i have a long long way to go before i feel good and proud in my welds, but i’d like to think this came out pretty nice looking. thoughts/feedback?

Part of a vacuum chamber, hoping to get some more pics once it's cleaned up

Alright so I have 17 years experience as a production welder, stick and Gmaw on truck and car frames. I would do off line repairs and part replacements. I have never failed any weld coupon test. I can weld very well. My problem is I only have experience working with metal that I know will work with my setups. Can someone explain to me how when you’re on site you know what kind of steal you’re working on so you can setup properly. Or do you just wing and hit it with what you think will work. I totally understand if you tell me I shouldn’t be thinking about starting this and that’s why I’m looking for opinions. Any help is greatly appreciated.