I guess it would depend on what you want to do.
If its for full on gravel racing events then you would want to use a heavier wall thickness. Tarmac could me made lighter,road so on.
Commonly chrome moly is used in about 1" Dont know about the wall thickness.
I would think a seamless tube would be the go. I have heard of cold drawn and hot but I dont know what the properties are.
Maybe google roll cages and suspension parts for some clues as to what steel they use.