Red_Dragon

Ok,I don't know anything about Amazon stuff but,I'd go with something like thishttps://www.mcmaster.com/products/steel-structural-tubing/shape~round-tube the picture is from Amazon but I have bought frame repair tubes from McMaster what ever it really would need to be structural tubing you won't regret it later it's cost a bit more but she'll do. There are other companies that sell structural tubing, sorry for late reply been having family sickness.

Okay! Sounds like good tubing for a quad. by the way. what kind of welder would you suggest to use?

Regular mig would work fine,or if you have a tig. Both probably would need to be on middle to low settings to ensure no warpage or burn through but all metals are different ,I usually take a small test piece and ensure my voltage and speed are enough then try welding.