It says that I need to have minimum 12" battery cable to connect to the free negative terminal (instead of just connecting directly to the terminal) and not to leave the system charging 'unattended'. It has an automatic cutoff when in 12 volt mode so my understanding is that I should be able to leaving it charging until Spring with no worries. I could really use some sound advise here.
That part of the instructions was written by their lawyer to cover their butts from potential lawsuits. The 12" cable moves a potential spark away from a possibly gassing battery and reduces the off-chance of an explosion. And stipulating that it must be "attended" means you can't sue them if the battery is so bad it overheats or runs dry from long term charging. All these things are highly unusual but conceivable. Given the number of careless or oblivious people in the world, the company has to consider that one of their customers is going to have a bad battery and act without reasonable caution. Thus the CYA.
So, make sure the batteries have electrolyte in them. If not sealed types, check each cell and top of with distilled water if needed. Then, with the charger powered off, connect the + lead to the positive terminal and the - lead to the negative. Since these are 6v batteries, the two need to be wired together in a series pair to make them into one 12v battery, just as they are in the RV. Then plug in the charger and observe closely for an hour or so, to make sure it is all functioning as expected. Check regularly over the weeks and months to be sure it stays that way. If the battery cases begin to get hot, unplug the charger immediately.
A two amp charger isn't going to overcharge a 200+ AH battery bank even if it runs for months. And there is nothing wrong with the little HF or similar chargers for this sort of maintenance chore. I leave one on a car we store for several months each year and it does a nice job or compensating for parasitic draw and self-discharge.
The OP first mistake is listening to the dealer. With 160 Watt solar system he should have no need for a battery maintainer
If the weather is poor enough that he won't be going camping, chances are there won't be much sun either. However, it's only a couple cloudy days now and then, the battery bank isn't going to discharge all that much either. It's a judgment call.