I've spent 30 or so nights in this over the last 3 years:
It's a 6 x 10 x 7 foot high trailer. I pulled out the walls and ceiling and put some hard board insulation in it (floor and back door are not insulated).
For Power: I put in a 15a input and wired 3 outlets. I also bought a 100ah deep cycle battery to run lights and a fan when I'm not plugged in. I ran two power stips: one to to the inverter and one to the outlet in the nose. I mounted those and makred one AC and one DC. So, that way I can just move the fan and lights over from DC to AC depending if I'm plugged in. I hooked a charger up to the battery so whenever I'm plugged in (genny or house power) it re-charges. Finally, I added one solar panel to the roof and ran to the battery to help it recharge when not plugged in. This last step was probably overkill. I could just use the genny to recharge the battery and I think that would have worked fine. But, having the solar is nice. I was out 4 days in one stretch and the battery held up fine running fan, lights, and re-charging my phone. I also added a trickle charger for the ATV so when I'm home I just plug the trailer in and the 100ah battery recharges and the ATV is on trickle charge.
For Heat: I ended out mounting two LP tanks on the tongue and using the MR. Buddy heater at night. The MR Buddy worked great. I could raise the temperature 50 degrees even on low in there. This is one of the advantages of having a small space to heat I guess.
For Cooling: Again, I had planned to use my heat/ac unit here. But, I found I didn't need AC. I was only in the trailer during the night and even in September it didn't get THAT hot at night. I bought a shop fan and that can run all night on the battery. That was enough to keep things bearable even during hot evenings.
Shelving I did a redneck special for shelving. I mounted 3 milk crates on a board and then mounted the board into the frame of the trailer. One one side, I use bungees to keep things in place. On the other side, I just mounted wood 1x6's on the front to keep things. I have utensils, bug spray, extension cords, toothbrush, toothpaste, electric bug swatter, etc. etc. in there. It's held up well.
Cooking/Eating: I found a small microwave that runs fine on my honda genny (2k watts). So, when I cook something I just have to run the genny. This is really the only reason I ever have to run the genny. I just bring easily microwaveable stuff in the yeti cooler. I keep some water / bottled drinks on ice in the cooler. I have the genny converted to run on propane.
Bathroom: You can see on the left side of the nose I have small portable toilet. You just put this bag in there (like a double bag) and do your business. It's kind of a zip-loc thing and it easily gets thrown away when you get back home. No mess.
Safety: I have a CO detector and a low O2 detector you'll see on the right up near the nose. I also have a small fire extinguisher mounted on the wall and one in one of those buckets up front.
Shower: Nothing. I just go home when I can't stand my smell anymore.
Organization: I use the etrack system on both walls to hang and secure all my gear. When I put the propane tanks on the tongue, I had to find a place for my spare. So, I mounted that on the wall inside. I also have a table that flips up off the wall. I would say having 7 feet really helped. I think if I had gotten a 6 foot high trailer I would not have been able to cram as much stuff inside. The buckets up front hold jack stands, some bungees, other misc crap. The red bucket is mainly just a trash can.
Sleeping; Just a fold way cot stored on one wall. I have a camping sleeping bag and 2 pillows in the milk crate / shelves.
ATV: ATV is tied down to the floor mounts. I found that so long as I run it dry when i load (keep it running, shut off fuel valve and let it die), the trailer doesn't smell of gas when I get there.
Here are a bunch of pics loaded, unloaded, set up to sleep etc.