Thinner walls on the WC. Thus, less R-value and weight.
Camping in sub-30 degree weather isn't a problem. Sub-teens with shore power, easy peasy. Below zero, without shore power, is not something I aim to do, again. As for the cab-over bed, heat rises.
Our AC unit is more than up to the task of cooling. We've camped in The Keys, in August. The inside of the WC, was positively delightful. We've also camped in Virginia, in August. Not really much different than Islamorada with VA's humidity and lack of ocean breeze. The Honda 2000 burned about a gallon every 3-3.5 hours, but no issues with the AC. We do need to turn the AC off while using the microwave, though. Not a problem.
Our WC 850 is a long-bed version, with no genny compartment. We don't spend our days in the camper, but I'll fire up the EU2000 to have a cool haven while changing adventure attire or to simply cool off. It cools down, quickly. A gallon in the genny, 6 gallons in reserve, with judicious use, nets a comfortable 3 days. I stash the genny plus a 1.25 glln gas can in the camper while motoring, and put a 5 gallon can on a hitch extender that has a welded-on step. The step is about the size of the 5 glln can's base, so it's easy to bungee/tie it down. If I used a receiver hitch tray/basket, I'd only load more stuff I don't need and add weight. The Harbor Freight extender/step works great. We use it for spacing the hitch-mount bike rack away from the rear door, too, when we're in mountain bike mode. It creates the space needed to open the camper's door, while providing a step area to spring off to enter the camper.
I don't use the hitch extender while pulling a 6x12 enclosed trailer. Two motorcycles plus support equipment, trailer is probably 3,000 pounds/350 tongue weight. The gas motor in my '13 F250, with camper package and 4.30 gears (plus rubber-baby-buggy-bumpers), does nicely. Factory suspension and jounce bumpers allowed a little more top-sway than the addition of Timbrens' baby bumpers and Torklift's upper overload-engaging blocks permit. Lowest I've calculated, with trailer, is 8 mpg. No trailer, back roads, doin' an easy 50 mph, I can see 10-10.5 mpg. Throwing the canoe on top seems to have little influence on mpg.
Basic tool bag under the truck's back seat. Multi-tester in the camper with a roll of duct tape, spare fuses, a length of stranded wire and extra batteries for the TV remote. Last week-end, I found some loop Velcro I must have thrown in the cubby at some point, too. Like an ol' grey-beard biker once told me, "If you know how to work on your putt at home, you don't need no stinkin' tool bag." Still, I carry some items that make me feel better. Folding lawn chairs tuck into the space in the cab-over between the mattress and window, with room to spare. While I'm not a weight-weenie, I keep an eye on the GVWR, tire pressure and lug nuts, loading heavier items low in the rig.
It's a work in progress. I make it up as I go along. I hope you have fun, finding your way.
One thing, though, no matter which camper you choose, make like Clouseau and inspect it top to bottom. You'll be excited, but get past that, forget about possibly being insulting to the dealer, and really look at it. Take the drawers out. Not open, out. Have a flash light in your pocket. Taking pictures, isn't beyond considerate.