What rules would you give a Plasma Cannon in 3rd ed. Space Hulk?

[Stormwind]

In a fit of madness I have been looking over the Dark Vengeance Deathwing squad and the newer Deathwing Command models from GW and considering making new versions of the Blood Angel squad in the original boxed game - with a couple of additions.

First, an apothecary Terminator
Second, a Chaplain Terminator
Third, a Terminator armed with Plasma Cannon instead of the Heavy Flamer, which is a new loadout in the latest DA codex. 

I find the "Knights" to look hideous and silly with giant flails and banners that wouldn't fit into the confines of the Space Hulk.  But these things above I think would be a nice change of pace.

Does anyone have any suggestions as to how a Plasma Cannon would work? Maybe like a Heavy Flamer without the ammo costs, but there's a chance after "x" firings it "gets hot" and might explode, killing the user? =-P

[Geep]

Hope it's no bad to reply to so old a topic. but one thing I'd suggest- rather than have an ammo limit, maybe have a recharge time (like Plasma weapons used to have). You could only use it once every 2 turns, or maybe every 3 turns.

If it was once every 2 turns I'd also reduce the impact of its flame-wall stopping movement. Maybe only the centre, targeted square gets the lasting flame bonus? It means you could use it almost with impunity compared to the heavy flamer, but you'd sometimes have to take less effective shots to block corridors and rooms.

[Jimmy Zimms]

Bask in first edition GW released rules for plasma pistols, guns and the "heavy" plasma gun so you should be able to take inspiration from there:

PLASMA GUNS and PISTOLS
Used by: Hybrids, Imperials, Eldar
Type: Heavy Ranged Weapon (w/ Area Effect)
Cost to Fire: 2 APs Hit Dice: 1 To Hit: 2
As soon as a plasma gun or plasma pistol has been fired, place
a plasma weapon counter beside the model, with the fired side
face up. At the start of that model’s next turn, flip the counter
over so that the recharging side is now face up. Then, at the
start of that model’s next turn (ie the second turn after the gun
was fired), the counter should be removed. While a model has a
counter beside it, on either the fired or recharging side, it cannot
fire its plasma weapon — this means plasma guns and pistols
can only be fired once every two turns. Models with plasma guns
and plasma pistols can’t be placed in overwatch.
HEAVY PLASMA GUN
Before a heavy plasma gun is fired, the player must declare
whether rapid fire or maximal fire is being used.
Rapid Fire: because this option only uses a small amount of the
heavy plasma gun’s vast energy reserves, no plasma weapon
counter is placed beside the model when it fires. It can fire again
in the same turn in either mode. Maximal Fire: this option
releases the weapon’s energy in a single all-out burst affecting
all the models and features in one section. The heavy plasma
gun has unlimited range but at least one square in the target
section must be within the firer’s LOS. Once the heavy plasma
gun has been fired on maximal fire, place a plasma weapon
counter beside the model as described above. Models with
heavy plasma guns cannot be placed in overwatch and cannot
move and fire.

[Stormwind]

Oh this is fab! Thank you for your replies! =)