It's easy if you know what you are doing.
First: How thick is your drum?
Second: What size wire you plan on running? This will play a factor on how well this drum will turn out and if it's the appropriate size for said drum.
Third: What gas you running with the wire? If it's in a thin drum, I would use GMAW short circuit mode of metal transfer.
If you are uncomfortable with welding on it, see if you have a Local CTC or College with a welding program that can assist you..
Also, be very cautious on welding on a drum, especially if it's sealed already; expansion of metal is dangerous, deathly dangerous. If you ware welding to seal it, the same applies, so be careful..