I've got a Maldol power antenna mount (the roof-mounted version of
http://www.universal-radio.com/catalog/hamantm/4219.html), which will be
mounted well forward to clear a (non-folding, plastic Cobra Explorer)
kayak . Why use the power mount? Two reasons: the Rube Goldberg factor
and the desire to have a decent range while still being able to get the
van in the garage or on the trail. I don't use magnet mounts anymore
because of the paint scratching that's almost inevitable.

The antenna I picked is the Wilson Flex 3'; it seems to be a good
compromise between length and ruggedness for my application.

Here's where I need help: What will be the cleanest (fewest holes) way
to mount the assembly on the roof & run the 3 cables (antenna cable +
small-gauge 12v + & ground) into the cabin? I'm not going to run the
cables in through the door seal--want it to be neater than that.

I plan to use an aluminum or stainless plate inside the roof to act as a
stabilizer--the 4 mounting bolts for the Maldol mount will go through
this plate, unless I can figure out a way to mount it somehow using just
one hole.  I can use NMO or non-NMO cable assemblies with the antenna &
mount via adapters. What will be the most leakproof way to get the
antenna cable (and the small-gauge 12v cables for the mount) through the
roof, preferably using one hole for all 3 cables? Are there special
grommets or similar fittings, or anything used in boatbuilding, that one
can use for this?

I've combed through a great many webpages and have talked to the local
2-way radio shop, but they aren't sharing their technique and won't take
on a one-vehicle job. Quote: "That's a weird van. Ain't never seen
anything like it before." Ahem.

Thanks to all!