Solar panels in a series?

[mitiempo]

Chip

Based on the bottom pic showing the 2 wires going through the deck beside the bimini attachment and comparing them to the countersunk bolt head I would guess 10 awg at the largest.

With the money invested and the expectations of the solar array I would use 4 awg for the works if you can find a way to route it.

There is nothing "solar" about a junction box - any waterproof junction box will work. Go to a good local electrical supplier, maybe a company that does things like garden lighting or hot tubs, they should have an inexpensive box that will work well.