I spent a good 6 months designing and re-thinking my "Dream" trailer.
The final design I found was trailer that was beyond just adding options to an existing manufacture's model, so I went custom and the results were fantastic. However, happiness comes at a price and in this case a big price, but I feel I have a life-time trailer for my needs.
Keys things I would recommend:
1. If a custom build, then taking the time to find a manufacture that is willing to work with you on getting what you want, not what they want to sell you. It took awhile to find the right mix of fabrication skill, a manufacturer that could make it happen in a somewhat timely matter and at a cost that wasn't at a Formula One level.
2. If you got the cash, I recommend Heavy Duty Aluminum construction.
I had 3 steel trailers back to back and the rise in use of liquid de-icers just killed them and this happened a lot quicker than I thought possible, mostly on the undercarriage and frame. To a degree, aluminum is suspect as well to road chemicals and has it's own issues with strength, but I didn't go Aluminum for light weight, I went that way because I'm lazy. It is purely for the corrosion resistance. My trailer is built like Brick S&%# house and probably weighs close to what a similar sized steel trailer would weigh, but I know if I can't wash it right away after a long dirty trip, it won't deteriorate like a steel trailer will.
3. My trailer is my garage.
Since I don't have a fancy shop, I made my trailer my shop. The entire front end is an outfitted work bench with all the power, lights, storage, tie downs, etc that I thought necessary. And what shop is complete without beer fridge as well. Sorry I don't have any pictures of the inside, but I can pretty much wrench on the toys in a nice heated or cooled environment. And then kick the toys outside for a place to sleep whether in the dunes or in the high country. Nothing fancy, just useful.
I can haul 4 sleds, or 2 Sides by sides, or a Jeep or a race car or all my ex-wife's stuff to the dump.
Of course my problem now is I have an itch for a new build. Funny how that goes.