, I also prefer the tin coated marine style wire. It is also nice that they have duplex and triplex options for 12V and 120V in the gauges you need in an RV. Marine style adhesive lined butt connectors are very reliable. I'd say that Ancor is the name brand for marine wire and butt connectors. It is what they sell at West Marine. But yes, this brand is expensive, even on Amazon. Digging around on Amazon, I've found other brands of this style of wire for less: https://www.amazon.com/gp/product/B00EADW6SW/
for example. This is mostly what I used in my van. I can't say about long term, but it looks good and has worked well so far.
For my 1/0 main cables, I used all copper welding cable. I bought it off Amazon, but I'd check electrical supply houses if you have the time.
I would not recommend THHN. It is just too hard to work with.
For connectors, I recommend a high quality ratcheting style crimper for normal stuff and hydraulic crimpers for 1/0 plus heat shrink. There is a guy on YouTube that compares pull out strength for various connectors. I'm pretty sure Ancor was the best, but all the ratcheting crimpers worked well. The basic type of crimper doesn't really work at all.
I am still working on finding a good solution for 12V plugs for things like the water pump, that I'd like to be easy to install and remove. I tried some inexpensive waterproof connectors from Amazon, but they suck. I recently ordered some connectors I saw electrical bike builders using. They look great, but I haven't had a chance to try them yet.