Two Chassis Amp - Wiring between them.

[NGW]

Hi Kevin and fellow TUT followers,

I am building a large combo for a local guitarist; Push-Pull 2 x 6CA7, 3 x 10" speakers.
Due to the large cab and wanting to keep the pre valves out of the speaker box, I have built it with two aluminium chassis (like some old amps).
One, in a separate compartment above the speakers, housing the Controls, Preamp and the PI. 
The other, on the floor of the cab, housing the Power Supply and Power Amp (the valves are shielded from the speakers).
This two chassis build is new to me and not something that I have done before now.

This build requires approximately 700mm of wiring/cabling between the two chassis for the;
HT for the PI & Pre (PT: 290HX = 356VAC at 420mA), Heaters, Chassis Ground, Speaker Ground, Feedback wire (circuitry is with the PI) and Signal from PI to PA.
I am going to use a relay, via a control panel switch, to switch the wall supply to the PS.

I have some ideas about which way to do this, but I thought I might ask what you blokes recommend, so I can get the best result, with no oscillation or noise and to ensure it is safe.
All suggestions gratefully received.

Cheers, Noel