There are a lot of small scale things we have added to our camper to make it less of a plain old box on wheels and more of a box on wheels that we are comfortable in. Most any of these projects can be easily repeated with the right materials and know how. Hopefully, these short descriptions will give you the necessary inspiration. I think your local hardware store should be able to handle the rest.
The original purpose of this box was to hold all of the various "hook up" components associated with RVs to save space in the underside storage, but it has sense become a trap for all things random from spare electrical cords to a caulking gun and insulation materials. I took a standard cargo toolbox from Lowes and bolted it to a couple pieces of metal stripping that I bent to the shape of and wrapped around the bumper. The stripping was then attached to the bumper using self-tapping screws. I eventually added an extra hinge to the box for more lid support. I keep a pad lock on one side of the box and a clasp hook on the other to keep it shut. This is an easy to get to storage box that keeps everything inside dry. Since doing this, I have seen many boxes that would have worked better, but this was the best option at the time.
The most important thing to consider here is the amount of weight your bumper can hold. Keep in mind, downward force and rotational torque are two different things. Standing on your bumper is one thing, but putting 100lbs on a mount extended out from your bumper is entirely different. Make sure your bumper can handle it before spending the money! Ours had a data sheet sticker on the back of the camper detailing the weight descriptions. We got the hitch from Amazon and the bike rack from Walmart and really like them both.
Some newer campers have automatic stabilizing jacks that do all of the heavy lifting for you. Ours does not. The rear jacks are especially difficult to use because they aren't even electrically powered but crank down by hand. Because our back end is often times a ways off of the ground, I created a pair of sturdy platforms to reduce the distance I would have to lower and raise the back jacks each time. These don't really add any stability, they just make a my job a bit easier. The platforms were built with a few feet of 2x6" and 2x4" boards. The top pieces are standard Lynx Levelers with the cap pieces.
Who would ever stack things this high? This mod involved a few carpentry skills, but not much - mostly just the time it took to stain the wood. I cut the desired length and width of the shelves as well as a few small support pieces. The supports were screwed in from the back side so none of the screws are visible. This easily double the usefulness of our closet by providing a much easier means of organizing our clothes. The stain I used for this and all of the wood related projects was a foamy spray stain I found at Lowes on clearance for less than a dollar a can. It worked really well, but haven't found any since so I'm glad I bought a few cans when I did.
I can't believe these don't come standard. I suppose this is just the right size hole to put a small waste basket or something similar, but a shelf for my alarm clock, chap stick, and phone makes a lot more sense. Originally, I built these with legs but have since gotten rid of the legs for more under storage space. The shelf are connected to support pieces which are screwed into the wall. The camper walls aren't incredibly thick, but the stock furniture was held in by three inch screws, so that is the size that I used as well.
This is really good for anything, but I built is specifically for my wife's collection of flip-flops. Although she doesn't wear them nearly as much as she did when we were in college, she really appreciates being able to pick out whatever color she wants without digging them our of some box somewhere.
Have you ever noticed how rusty the ends of the bumpers are on older campers? That's because this is where a lot of people keep their sewer hoses. Not only does this cause the rust, but it also creates a gross smell in the back of the campers because the remaining liquids in the hose have no way of draining. I took a large black PVC pipe and attached it to the underside of the camper near the sewer connections using a few pieces of metal stripping. The pipe is slightly angled and the end cap has slits so that the liquids have a way to escape. The only thing I should change about this design is the small cap that seals the pipe. It could potentially pop off while the camper is in motion, and the sewer hose would become roadkill... A better idea would be to fit a screw on cap for the end of the pipe.