I haven't bagged any layups as big as a boat, but it can easily get messy...
Although the bigger size may make some aspects easier (than for instance a 3 foot long female mold for an airplane fuselage). But I imagine the big layup would make more hands VERY useful! And the second pump may help too, pumping down the layup in the first place, and while you're working to get the leaks plugged, it will keep the whole mess tight. A third set of hands might be good for operating the digital camera (hint hint hint) so we can all see how it's done!

Incidentally, sometimes, when first pumping down the layup, I've stopped the pump after the air is mostly removed, but before any real vacuum has been developed. This is the LAST chance you get to reposition anything. Even then, it's hard to see what you should be doing, since the glass is buried under so much material/peel ply/bag etc. It's a lot different than when the glass is right there in your face and you can see every little thing. Not being able to see makes that initial resin spreading onto the cloth, and layout of the peel ply very important. On the other hand, you want the bag big enough that it doesn't distort the hull shape as it pulls down.

All I can say is PRACTICE... Make a small test panel... Dry runs even... And preparation. Make sure you have EVERYTHING all laid out, ready, cut to the right size, and enough to do the whole planned job.

Another sub-thread mentioned having a big enough bag for getting flow from the whole surface and evacuating all those tiny bubbles... IMHO, Bag fit isn't important since it flattens out immediately anyway, even wrinkles collapse to flat ridges... this is what the absorbent layer is for! If you use a THICK absorbent layer, all gasses in the bag flow up out of the layup, into the absorbent layer and move through it to the pump line. Make sure theres enough absorbent material that it wont completely saturate with excess epoxy. If you put too much in, it wont hurt anything, and you can rescue any that comes out dry and use it again!

Finally, it may be obvious, but be CERTAIN that the force of your vacuum is not loading any structure (meaning just be sure the vacuum isn't pulling closed any spanned openings).

Its fine with me if anyone wants to move some of this over to wiki... Just omit my email... I get more than enough trash email already.