[Arran]

 A 3'' pipe cutter is defiantly the easier way to cut these sorts of cans open, from there you can use one of two methods to join them back together, I picked up a China cheapy for just that purpose. You can cut the can 3/8'' to 1/2'' up from the bottom, and used the Morzh (Mike) method of friction fitting the top of the can over the lip you left at the base. The other way is to cut the can higher up maybe 1/3 to 1/2 way, and then either tape the two sections back together with aluminum duct tape (not the Red Green plastic duct tape) or come up with a coupling to fit on the inside of the can, the tape method is good enough if a cardboard sleeve goes over top, or you are not fussy, or it will be obscured from the back of the chassis. 
Regards
Arran