Still not sure what method I'll use to secure to the hull, oil bath or epoxy in butter dish. But will re-examine the 'under sink' area. Awfully tight with 2 thru-hulls and 2 bilge hoses (auto pump & whale backup). Getting a hammer in there to pound down a plug in case of emergency would be tough.
The engine compartment has room, but difficult access. Plus lots of vibration from the engine (I'll be re-powering next year) and associated heat and blow-by exhaust fumes. Not electrical friendly.
I've already drilled wire-chase holes for the water speed 'ducer coming aft from the forepeak locker. My strongest inclination is to install depth adjacent to this 'ducer.
Will re-evaluate in a couple days when the holding tank replacement project is done. Didn't realize that the Ronco tank & thru-hull would be so difficult to install. Had to glass over the original thru-hull hole & install the tank prior to re-installing the thru-hull fitting. Good thing is I'll have space to mount an in-line gusher pump & y-valve in the same compartment, under the starboard settee. Will be glad when this is done.
Tough project. Couldn't see how difficult it was going to be until I hauled out and removed all existing pipe/tank/thru-hulls. I've been taking pictures, if anyone's interested I can share when done (hopefully soon).