Bruce (and SC), I value your expertise and ideas. You are both pioneering the use of solar power on a small camper. You each share your expertise, ideas, favored solutions, successes, and some missteps to avoid. Thank you very much.

This is mostly new to me. I'm trying to design a solar and electrical system to best meet my needs and capabilities. There are many different ways to do it that can work well. And some that might not work well, may waste money, or may be unsafe...which I want to avoid doing. These systems are costly. Finding the right balance of readily available parts, cost, quality, usefulness, and simplicity or complexity is not (always) easy. Hopefully others may learn from this too to design their own solar electrical system and avoid some pitfalls.

Most pre-packaged RV solar systems I find available are very expensive. Many do not fit my wants and needs for a teardrop trailer. Some have parts of questionable or inferior quality. So a well thought out custom system is what I want.
If my roof was a little wider many, higher capacity, solar panels are available. Many cost less than the 125 watt panel I plan to use...which is frustrating. I would use a higher capacity panel if I could find one that fits my roof and budget. I gave serious consideration to using an mppt controller to get the highest possible harvest from a 125 watt panel since I cannot find a solar panel with a higher output that is not too large (long) to use.
Land your solar charge wire on a 20 amp fuse in the DC distribution section of the PD 4045. Then you have a fuse and you don't have to worry about another terminal corroding off.

was a twist and turn idea for me trying to get to the bottom of what you were suggesting. Mixing metaphors...Its still foggy. I want a PD4045 but have not purchased one (yet) so have still to learn its ins and outs...which seem to be somewhat confusing to many folks here.
There are so many twists and turns to think about. OK, a new turn. I can wire a
Morningstar "Sunsaver" 12 Volt 10 Amps Solar Panel Charge Controller positive output with a
Mini Blade ATM Inline Fuse Holder connected to the input side of the
Hi-Amp Surface Mount Circuit Breakers - Manual Reset (Switchable) in the battery compartment, instead of directly to the battery or PD4045. Easily done. The positive power from both the solar and battery can still be safely switched on or off by a
Battery Cut Off...without an additional switch. Easy peasey. Less opportunity for damage from terminal corrosion.
New thought. Never have used
Anderson Powerpoles. A pair on the incoming hot lead to the solar controller might be handy.
I probably would have bought "jelly rings" from an auto parts store to protect battery terminals. Now I know to ask for battery terminal spray. Thank you.