> any thoughts on taking the entire trunk, 
> wrapped in mesh/screen, vs. trying to 
> extract the bees on sight?

If you can get use of the equipment for free or cheaply, taking the whole trunk is quick, easy, and allows you to split the trunk and  remove the bees at your leisure, well away from kibitzers, or, take the slower approach, and let the bees move up into boxes placed atop the trunk, and roughly sealed with pallet wrap or expando-foam to the top of the trunk.

I did this several times, but only because the NYC Parks Dept has a great "forestry" department with chainsaw artists, and a truck with a boom-and-claw to grab trunks and set them down gently once they are cut free.  If you do not have access to power lifting equipment, you are mixing height, chainsaws, testosterone, heavy wooden objects, and bees... not a good mix.

Now that it is winter, you have the luxury of time to work out the extent of the cavity with a thermal camera, or (my favorite) a 1/2-inch spiral wood-boring bit.  Experimentally drill both below and above to make sure that you have solid wood, and can cut well above and well below the colony.  If you drill into the cavity, plug the hole.  If you don't, mark the trunk cut-here-line with some paint.  You want at least a good 6 inches to a foot of solid wood above and below the cavity for transport without tragedy.

 I would slap a large hunk of metal screen (not the plastic stuff, the bees will chew through that in minutes while you drive) over the entrance, and staple it to the bark, and then wrap a dozen go-rounds of pallet wrap to seal and cover the edges of the screen, yet still leaving the screen open to allow some airflow.  This is optimally done at first light, so as to minimize "abandoned" bees hovering around after you leave, but I have also left "catch boxes" with lemon-grass lures and a few frames of comb on site to collect the strays for pick-up later that evening.

You can later cut off the top to expose the cavity if you want the colony to move up into boxes.  The combs are attached to both the ceiling of the cavity and the sides, so very little damage results if you take care and stop cutting with the chainsaw once you get close, and switch to a bow-saw (or one of those Japanese framing-timber woodworker saws with the large teeth) for the cuts that expose the colony.

Splitting the trunk is something best done well away from civilians, as this is a violent way to remove bees, and the bees have definite negative perceptions of people breaking their home in two.  If you intend to split, using wedges is yet another art form, best to call in an experienced guy, and outfit him with a beesuit.  Split-open colonies are a race, as you may attract robbers if you don't work quickly, so set up boxes, frames and #10 rubber bands in advance.  A serrated bread knife is your best friend here.

A tree fell up at the Bronx Zoo in an early 2000s storm once that was home to a very large colony of bees, but the tree was blocking the path from the giraffe barn to their pasture, so we had to work in the rain to clear as much of the tree as we could, and ended up with the tree at a 45-degree angle with one end of the trunk against a sturdy fence.   We lifted up the low end of the trunk, and slid sections of truck under it, to make a waist-high trunk with the spilt facing upward, and pulled comb under a tarp to keep the rain off.  Got lucky, actually came across the queen, so the job went quick.   But pulling bees out of a tree in the rain is not my favorite beekeeping memory.  And giraffes are lots of fun to feed, but they have horrible putrid breath. 

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