Tom-
Looking at the schematic book for our '06 Monterey, I'm sure the Control Module you refer to is for the US Gear brand of tow brake that some, if not all, Beavers were prewired for at the factory; probably through some special deal Monaco had with US Gear that encouraged customers to buy a US Gear brake system for their coaches. The Control Module image looks just like photos you see in US Gear ads. Unless you are using a US Gear Tow Brake on your toad, I'd ignore that part of the diagram; and even if you do have that device, I wouldn't think it had much to do with your battery charge endeavor. I have to agree with Gerald though, if set up right, you shouldn't really have to be charging the toad battery. If I was pulling a trailer with some electronic devices in it dependent on constant onboard battery power, and in need of a charge source, then I could see tapping the black wire in the female tow plug.
Our coach owners manual does show a diagram of the tow plug receiver (pg 33), and refers to the battery (hot) prong you refer to. As to your question on the 20 amp device icon, I'm no master electrician, but I'd guess that to be a Circuit Breaker; if you look elsewhere in other diagrams in your book, you should see similar icons with names attached such as "CB27" or "CB18", etc. Some of these are located in the electrical bay (front of coach, driver's side) and may be identified there, but our diagram in question doesn't locate that 20 amp circuit breaker for us, nor does it assign it a name like the others, so it may be "in line" somewhere, who knows; it could be in the electrical bay, but you might have to rummage through 1000 wires and looms to ID the wire to it, and there's no point to tackling that job for your purposes. At any rate, it apparently would protect the coach from any catastrophe that occurred to the attached battery charge circuit to your toad, and that pulled more than 20 amps.
Hope my 2 cents is of use to ya.
-Joel