Fighting a dragon in its lair is a fairly widespread situation in dungeon fantasy adventures, and it often becomes a climax of a dungeoneering raid.
Say, our heroes are going to fight a dragon. Let's make several assumptions:

1. Heroes are going to fight a fairly strong, but not invulnerable dragon. Dragon's armor is tough, but not unbeatable – fighters and archers can (perhaps barely) penetrate the scales, or maybe they can target known weaker spots with a "called shot" (targeting certain hit locations) at a penalty.

2. Dragon's main attacks are fiery breath (cone/area-effect, most probably), striking with his tail and claws and trampling with his body. These attacks are dangerous, but not the ones that can easily destroy a building of kill a unit of infantry in a split second.

What I mean is it's not a "Smaug" type of dragon that requires a mandatory hit at an obscure hit location with a ranged weapon (because no one can get close to him unharmed). It's rather a normal "dungeoneering" type of dragon, which is fun to fight – not a flying, nearly invulnerable killing machine. Let's assume something like DR 15, Innate Attack 6d burn (Cone) and availability of targeting Chinks in Armor (or some sort of armor gap at least at -7 after applying SM), but I'm new to running fantasy GURPS games, so please feel free to change these assumptions if my version is too weak.

3. Heroes will have to beat the beast down. There's no sort of a trap they can lure dragon into. There's no specific trick like "hold him for 30 rounds while I'm casting an ultimate dragon-killing spell". They will have to use more or less "standard" attacks. At this time Luke Skywalker will have to fight the rancor, not cause the gates to collapse onto its skull.

4. Battle takes place in a chamber of a dungeon, so dragon won't be able to fly around like mad.

Now, how the heroes are going to fight the dragon rules-wise in GURPS?

With more simplistic fantasy-oriented (or fantasy-compatible) role-playing systems I get a clean picture of the fighting process. Heroes engage the beast (fighters, barbarians and paladins will want to get as close as they can, while archers and mages may hold the distance), make attacks (trying to beat Armor Class/Defense/Parry/whatever), cause damage, use save throws/evasion/whatever to evade fiery breath, use their own Armor Class/Defense/Parry/whatever to defend from strikes until the dragon (or the heroes) will fall.

With GURPS it's more difficult for me because I'm used to its "simulationist" feel. But I well know system's flexibility, so I belive it's possible make fighting a dragon simple and fun in GURPS too. I'd like to avoid "one-hit kills" by a dragon while retaining pressure onto heroes. My issues/questions are:

1. There's no "save throw" in GURPS against area-effect attacks aside from Dodge in a form of Dive for Cover. Average damage from 6d burn Innate Attack is 21. Jumping aside divides the effective damage by 3, since hero is now further away from the middle of the cone. Say, paladin wears DR 8 breastplate armor at his torso, divided by 2 for Large-Area Injury. So typical damage will be 7-4 = 3 HP against armored hero, or flat 7 HP against unarmored one (provided Dodge was successful). Also it always leaves the hero prone on the ground. Looks playable and fun (damage caused, but there's no instant death of incapacitation), but does it look plausible rules-wise, in GURPS sense? Opinions invited.

2. Is it OK to ignore dragon's posture and facing? I mean, if beast's most vulnerable hit location is its neck or breast, he can avoid damage by simply turning away from the heroes every turn or holding its head high. I'd like more abstract approach towards fighting such a huge monster. Doesn't it feel too un-GURPS?

3. I'm gonna ingore weapon-breaking rules, I think. Taking that into account, can heroes safely parry dragon's tail strikes and slams?

Also I appreciate any tips on running combat against big, strong monsters in GURPS.

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