Hopefully we have some hardcore strobe lighting jocks here who can help out on this. I've asked on a couple other boards and gotten some responses, but nothing authoritative. I'm hoping for something more than "bracket" or "take a test roll", from somebody who really knows lighting.

Next month I'm going to be shooting some interior shots in a rather unusual venue. Groups of people in meeting and dining rooms in a smaller restored "boutique" hotel, with dark wood paneling and darker earth tones. Ceiling, IIRC is maybe an ecru or a dark eggshell at the lightest, quite warmish, IIRC, so bounce flash will probably not be an option. Available light is poor, mixed, and quite warm.

Here's the problem. To get these shots I'm probably going to have to use the Sigma 18mm ultrawide. (non fisheye)

I have two flash units, a Vivitar 2600, which is probably out of the question. Then I have the hand-me-down resurrected Sunpak 120 flame-thrower. I know it won't light the scene with the reflector, even at the so-called wide-angle position.

I can do it bare-bulb, no reflector, either aiming the bulb upward or pointed forward.

The problem is, I have no clue as to how to expose for such a situation.

Can auto mode be depended upon in a situation like this? Or should I use manual and do guide numbers? If I do guide numbers, should I try to adjust for the 360 degree coverage of the bulb?

Yes, I looked at TFM, and it didn't really say much about bare bulb mode except that you can do it.

Anybody shot a bare bulb unit in a similar situation?