Where to mount rear diff temp sender?

[RanchoRunner]

Hey everyone,
Interested in getting your knowledgeable input:

I tow a 5,000 lb. trailer, and will be making a 2,500 mile trip next year. After reading the article in the June Off-Road Adventures (4WP magazine) entitled "FINESSE -- Towing Gears, Towing Traction, "A Guide to Axle Mods with Towing in Mind", I am going to get a Rear Diff Temp Gauge to monitor the rear axle temps when towing.

My question involves how and where to mount the sending unit.

1) Replace the fill plug with a bushing and sending unit?
2) Replace the drain plug with a bushing and sending unit (though I'm wary of it hanging down and getting broken off while off-roading)?
3) Drill and tap a hole in the axle housing? Then, near the top or bottom, above or below the fluid level?
4) Drill and tap a hole in the carrier housing? Then near the top or bottom, above or below the fluid level?

I know that the Mag HyTec covers for other vehicles put the sender unit boss at the top, but where it'll get bathed in fluid thrown off the ring gear (the hottest point)...

With the Toyota design, I'm not sure where the best point is...or should I take it someplace and have them install it?

BTW, the sending unit is 1/8" NPTF thread...

Thanks