Most people ignore fuses before controller, some have switches for convenience when they have to work on something. Such a need is infrequent, and I just go up on the roof and undo the MC4 connectors on panels in this case. Switch - if you choose to install it - can be AC or DC, not too important as long as it can support the current.
But... Senor Mex pointed out recently - and I have to agree - that there is a possibility of a short between panel wire and ground. 30A is a lot of current through the trailer structure. This fuse should be close to panels.
After the controller you need fuses or breakers for sure. I use Big Baby breakers box with 12V breakers.