I welded aluminum in welding school 4 years ago lol nothing recent or since lolOne thing, you won't have to be concerned about it being top heavy. 66 gallons should hold you for a while with your new tractor. Can you weld alum if you need to?
I cut propane tanks alot I fill them with water and dish soap.Looks good to me. Aluminum welds good with the proper rods. The danger is blowing the tank up from the sparks. I know a guy cutting up old tanks to sell for scrap and one blew up in his face. He made it, but it put a hurting on him.