It looks like you did a Good job getting the Roof on strait not an easy thing to do and it took Balls to attempt it!
Again I don't know what Mig you are using or what your settings are or what wire your using or what thickness.
For Skins I like to use my Tig or Gas generally so I can Plannish out the Bead while its still hot. A Gas Bead and Tig bead are soft and can be worked, A Mig bead is Rock hard and hard to Plannish and can Crack if over worked.
I prefer Hammer welding when It can be done watch this.
https://www.youtube.com/watch?v=Rv5bKXJ3kEM&t=17sWith a Mig welding Sheet metal is not easy! What works for me may not work for you!
I like .030 wire not the .023 stuff, I think the .023 is too Hot myself even though your using a lower setting and its a thinner wire. Why I have no idea I just didn't like it myself.
There is some Mig welding wire made by ESAB called Easygrind its a lill softer I think, Its probably just my imagination! in my mind But I like the stuff. I am out of it right now, It can be hard to find, ESASB on line is best to find it if you wanna try it.
I have learned to use My Tig for most all my needs and mainly use my Mig for heavy stuff or stuff I am just gonna leave as is or grind away.
If I am forced to use the Mig on Skin I use a Little higher heat and wire speed than directed in most charts and use a repeated ZAP zap zap method, allowing the metal to air cool after a half inch to one inch depends on what I am welding and I NEVER use a blow gun to cool it. The heat of the welding and shrinking of the bead itself causes warping not the residual heat some may disagree but opinions are like Butt holes every one has one! Some STINK!
There is A lot of False information and Myths repeated by mouth and on line about a lot of different topics by people that think its the way to do something as it makes sense to them and others when in fact they are false truths.
Like you need a Gap for all welds when in fact that is not true. When welding Thin metals such as sheet metal I think its best to use a ZERO gap! But in reality the use of a Gap really depends on what your welding material angle and fitting joints.
But yet you can find cute little panel clamps on the market that force a Huge gap between pieces. This video shows these
https://www.youtube.com/watch?v=No4RKNa_jqM&t=877sI tried these clamps and I pitched them out of my shop! long before this video was ever made! They Suck! for me I don't like them and I don't use them! But that's Me!
My point being Do your own research don't be afraid to try other things or new things don't always believe what your buddy, brother, or Brother in law says or what I say! What works for me may not work for you! No two people weld exactly the same nor do they use the exact same equipment or materials! You have to make it your own! What works for you while you may follow some basic guidelines but make it your own make it work for you. When you do that then the world of welding opens up.
Another big falsehood is how a Bead looks! way to many think it needs to be a pretty
stack of dimes when in fact its what the back side looks like that's important!
Do you have complete fusion and complete penetration! Did the metal need to be Back purged? Was Back purging used when it should have been? Even Mild steel can benefit from back purging! its not only for Stainless, Aluminum Titanium and other exotic materials. Is it always required heck no but I have have done many welds that I wish I had!
Using Heat sinks and Heat dams
Another It has its Place when to use and what to use its one you have to figure out for your self. I myself have tried it on Skins I DON'T LIKE IT! It sucks the heat away!
Another myth I had to bust for myself! others May argue its the cats meow and it works for them! Great! It doesn't work for me or all of us! and by the way they don't show there beads OR the Back side of the bead! until after they grind it.
The Most important when learning: pieces to be welded keep Clean front and back no rust no paint no grease or oil wipe with Acetone before welding, Keep your Stick out short! watch your torch angle stay within recommendations.
Welding is a Skill and a Art with a Lot of Science involved any Skill requires a great deal of practice the Art follows creating your own way! the science is Metallurgy. Study the metals and welding rods gasses temps not all are the same!