Bob,
A lot will depend on how much you have drawn down the house bank. If you don't have a monitor (not just a voltmeter) you will never know. While 3~4 hours of driving will do our coach well enough, I have also optimised the system. You are just going to have to try it and see. We have electric refrigeration and we still do alright, but we pretty much only stop for a night and rarely at a crampground.
Your two Gr 27s will do you no favors. When time comes for replacement, switch to a pair of GC2s.
Matt