Chassis cutting

[Hog]

This is not something I've made yet, but hopefully I'll soon have something worthy of this section.....

In the meantime - and this may be a dumb question - I've got to cut an alloy chassis square across the middle as part of what I'm building.

Question is - what's the best method to ensure a dead square 90 degree cut across the chassis? I'm a bit crap with a hacksaw - more hack than saw if you will - and don't want my project to look like a bodge job.

Any ideas other than take it to an engineering company and asking them nicely if they'll water or laser cut it for a few quid?