Desert Rancher,
Your location is exactly what I had planned to do with mine. I am picking up my ATC Ocelot on Friday. I had wanted to get the battery mounted first and planned on the same location as yours but the guys at ATC said it would be in the way of the turnbuckle. If I could be more patient, I would just wait until I return home with the ATC and decide then. My current battery is even smaller than yours, it is a 55 amp AGM.
I prefer to mount the battery to the truck rather than in the camper to save space and because when the camper is off the truck, my secondary battery can still be used to power my communications radio, flashlight charger and walkie talkie charging base.
For my ATC, it is a shell model, I need only power lights. I may make those all LED which will allow me to use an even smaller battery such as one of those nice, slim 18 Ah units. I suppose, once I have the camper here, I'll figure it all out.
Gene