Re: DIY tank... even if you can't weld
Who are you asking in relation to what tank? For my tanks I use a brass hose coupling along with a brass hose cap. Home Depot and other building supply stores carry them. Half of the threaded coupling gets the threads ground off (the end which fits into the tank) and then the coupling gets soldered to the tank (either steel or copper). The brass cap gets a small vent hole drilled and on the inside of the cap a small baffle is fitted to keep gas from splashing out. This makes for a nice looking and inexpensive filler and cap.
Someday when I grow up I will probably lose interest in toys with wheels, but until then...