Oh I have such a good answer for this one: a camper van.

TLDR: I wanted to travel the US and explore national parks in a camper van. I'm handy as a builder and knew that I could, technically, build everything. Turns out that the challenge wasn't in the technical aspect but rather the sheer volume of work involved.

A little more detail: Having grown up around 4x4 vehicles, I wanted something four wheel drive. No full-sized American made vans come from the factory as four wheel drive. Even if you find a new 4x4 van on the lot, it will be an after market conversion. This means that they're harder to find and, thus, cost a bit more than your typical 4x4 truck. But I was determined. I found a 1987 Ford Econoline in rough shape for around a grand. I bought it, named it "Polar Bear," and set to work on it.

One of the biggest setbacks for the project was the ongoing expense and hassle of repairing an old van with a custom conversion. I learned more about automotive mechanics with this vehicle than anything else I've owned. Still, a lot of repairs were well beyond my scope and I ended up spending tens of thousands of dollars rebuilding various components. Repairs were a near constant problem and this drastically slowed my build process.

Another hitch in my plan was fuel economy. Polarbear would take me a mere 9.5 miles on a gallon of gas. With a 3-speed transmission, the engine was always running at a high RPM. The alternative factory transmission with an overdrive wasn't as strong as the 3-speed and the gas mileage was only nominally better. After extensive research, I learned that a manual 5-speed swap could be done and would increase my MPG to over 20. However, with all of the expense and hassle of installing a clutch, I never took on this endeavor. Ultimately, I never did that national parks tour. I did, however, go a whole heckuvalotta cool places.

The camper conversion, which was supposed to be the focus, took me a solid ten years to finally complete. There are a lot of rather sloppy looking camper vans in the world and I really wanted mine to look good. This meant taking time on the details. And oh my, where there details. Unlike a box truck, a cargo van's walls are all continuously curved. Cutting wood to smoothly fit the curves of the walls is tricky and takes time to figure out. I also learned a ton about automotive and RV electrical systems in the process. When I began, I imagined a very complex system. I quickly learned that the more simple the design, the better the design. Everything has the potential to break and the more complex it is, the more likely it is to break. In the end, I decided to entirely skip water pumps and simply went with a gravity based system. And despite having a propane tank mounted to the van, I opted to use a portable camping stove instead of running more propane lines. In my opinion, these were good decisions.

Over the course of ten years, I spent enough money to have bought a nice completed rig right from the start. At the very least, I could have purchased a completed 2wd camper and had it converted to 4x4 for far less money. This would have also given me a more modern 4x4 drive train and suspension.

Still, I have no regrets. What I learned was priceless and the adventures I had along the way are some of my best memories in life. I finally sold the van last year for almost 10x what I paid for it - but far far less than I had invested in it. The following link is the build thread I posted to the Sportsmobile Forums for anyone who may be interested in seeing what she looked like:

https://www.sportsmobileforum.com/forums/f24/polar-bear-1-a-...
(the last page has the final pictures)