Thank you all for the feedback. I am used to working with the big heavy batteries. I used to have a small electric car that ran on eight of them (plus a 12 volt for accessories). I just bought a used 2003 Scamp
16' Side Dinette instead of ordering a new one (I lucked out to find one near by), so part of my question was answered. It already has a 12 volt for now. I will modify the trailer to add in two 6 volt batteries to replace it. I will have to deal with the increase in tongue weight
and will consider how I do other modifications to keep it in balance. They do make double battery boxes, either side-by-side or end-to-end. Once I have the trailer here to work on, I will figure out the best way to arrange the tongue to fit it all in.