I’ve never heard of an Aerolite “7” so can’t help you with the specifics, but I can give you some general info.
Google what an RV furnace looks like. It has a very distinctive exhaust that will be visible in the sidewall on the outside of the trailer. Note where that is and look inside the trailer in the same spot for a removable panel (possibly w/air vents and held in by a couple of screws). The furnace is behind that panel. Mine is behind a panel right under the frig.
The connector for the propane should be readily available from any RV dealer. Take some photos of what the hookup looks like on your trailer and the parts guy should have whatever you need.
Sealants - once again, tell the RV dealer what you want to seal and he can help you out. Stick with “dicor” products and you can’t go wrong. Also, google “dicor” on advice for product along with preparation instructions and installation advice. Remember, meticulous surface preparation is the key to a successful outcome.
99% of the time the battery is on the tongue of the trailer.