AH on duel 6's and duel grp 27's are near enough to be considered equal. What you lose with duel 6's is commonality with your truck's batt if you ever need it in the boondocks and the ability to power the camper if one batt dies.
The WFCO is considered a poor charger here since it is very hard to get it to go into "boost" charge. That is something you'll need if recharging your duel batts from 50% SOC or below in a reasonable amount of time. Do a search here on "WFCO" and you will find the cons and suggestions for replacement.