Re: "Tracer" MPPT controllers from China
I will only say that you get what you pay for....I have installed several dozen boat, rv and cabin systems, and have yet to have a blue sky failure...as for the cheap stuff, it lasts only a few months in a rugged environment, and has ZERO customer support..if it works out of the box at all...I have quit suing the "cheap" stuff as it is not worth the troubleshooting and self doubt that an out of box failure causes....and I have to pay for a second or third or fourth trip back out of my pocket. And several days/weeks delays for a replacement.
IMHO, you are putting the cart before the horse, and need to do a power budget, I am afraid that the a 20 watt panel will not be up to your needs.
Once the power budget is done, then you need to look at a proper marine installation, and I would suggest that you either postpone the project or get something between the top and bottom price points you have in mind already.
Best of luck, and I am sure that you will get other thoughts here as well.