You are definitely correct that lighter loading, as you have stated, if that is all you expect to pull, would definitely reduces how much credence to put behind my concerns from above.

I'm an electrical guy so I end up geeking out way too much on this sort of thing.

The fact that you aren't trying to unstuck it while buried in mud, or pull it fully loaded straight up the side of a tree, and just going across pavement/slight elevation rise may even allow you to get away with using a healthy deep cycle that is isolated. I would be interested to hear about your result if you try it.

One thing you may want to look into are these sort of hybrid batteries that aren't fully deep cycle but not quite a starting battery. They are often marketed as being deep cycles, but will have a much higher CCA rating than normal deep cycles and cannot take the deep discharge abuse a normal deep cycle can withstand. I often think of them as the fake deep cycles since these really are not what you want in your RV since they wont last like a true deep cycle but they aren't what you want as your starting battery either. I have no idea why they exist but maybe they are useful here.