Not to be a party pooper but... I have some serious concerns about the structural stability of what you are building. You have been using an 80-90 amp 110V MIG welder. On 3/16" steel, Miller's welding calculator calls for 160-170 amps and 1/4" calls for 180-190 amps. 110V MIG's are notorious for giving welds with little to no penetration. In my opinon, 110V MIG's are not good for anything over sheet metal. Couple that with the dynamics stresses of a trailer going down the highway, and you have a recipe for disaster. I strongly urge you to consider letting a professional do the welding with the proper equipment so that no one gets hurt. Again, not trying to rain on your parade, but it needs to be said.
A nation of sheep will soon have a government of wolves - Edward R. Murrow