MIG is definatly the easyest way. tacking all the way round till the whole thing is sealed is the best way. depends on what sorta quality repair you want thought.
most rust repairs or panel joining i do myself, i weld with any oxy welder. purley because you cannot metal finish panels when using mig because is makes the panel to brittle and un- workable. and yes oxy does put out alot of heat but when done propery it is the best method. mig is i lot quicker thou