I'd also recomend you assume the trailer weighs more. The lightest 7000 GVW car trailers I've seen are open-deck models which weigh in ~1650 lbs... Most 7000 lb GVW trailers with a full deck weigh 1900-2200 lbs.
I've been towing my '98 XJ (built for wheeling) a bit with a WK CRD on a 7000 lb GVW trailer... I've taken 1 long trip (~325 mi round trip) with it through fairly hilly country (highways and back roads) and several short trips on local country roads (15-20 mi at a time). I didn't get great mileage (~14 mpg), but I didn't have any problems going up or down hills at 70 mph on the highway either - I was passing other cars / SUVs on the uphills if I wanted to.
I figure the trailer I have (~23' long) is ~2000 lbs with the XJ + gear (tools, camping gear, etc...) the total load probably comes in around 6500 lbs, or a bit more. With a weight distributing hitch the WK + loaded trailer handles really well. With that much weight you need trailer brakes on both axles.
The ZJ is slightly heavier than the XJ, but not a lot... The WK or XK can tow it, but don't plan to be too aggressive driving. I don't know how well the Hemi tows, but the CRD is awesome!
1998 XJ - built for offroading
2007 WK CRD - DashHawk, for towing the XJ