Thanks, people. A lot of useful tips. Soldering is not my forte, so I'll have to settle on dielectric grease under the lugs and on bare ends. Genuinedealz won't put any grease under lugs, though.
SMK - yes, the bus bars have 2 holes up to #1/0 size and 4 holes up to #6 size. I was worried about braided #6 fitting in #6 hole because there are only two #1 holes in each bus. Trimming the wire (if necessary) has already crossed my mind.
Those are very small terminals, both Pos and Neg busses fit inside Big Baby breakers box from the same Midnite Solar. The box is mounted in the trailer pass-through storage (like a basement in 5-er), so it's not quite "outside" though less protected from salty air and humidity than inside of the trailer.
Bare wire ends on solar controller are inside the trailer, the controller is my room-mate, he lives in the bedroom.