I'm just wondering how others have secured the brake lines on a live axle?

I'm in the process of rebuilding a Striker with an Escort axle and the last owner had them tie wrapped in place. The car will need IVA so needs to be able to pass so has to be done right.

Just curious how others have fitted there's.

Apparently large metal worm drive hose clamps are ok, although I'd rubber line the pipe first. Others have welded drilled metal tabs to the axle allowing you to use p clips.

Mine are held on with metal cable ties clamped onto bits of rubber hose that I split and pit over the brake line.

Would it not make more sense to mount to the chassis then flexis direct to the back of the drum/caliper?

Probably, but that way you have two flexing bibts instead of one, so greater chances of failure. I´m using a live axle, so will be using a flexi from chassis to diff, then hardline to the calipers...
HTH