Looking to get into a diesel (not new) to use 3000-5000 miles per year to pull the boat, sleds, and enclosed trailers. Any issues with letting a diesel sits for periods of time between use?
To answer your question, it depends. I have owned diesels since the early 80's. I currently have two diesel trucks, seven diesel tractors, and a diesel skid steer. You can let them sit idle for a period of time (Most of my tractors sit idle through the winter), but if they sit idle for a couple years you may have problems with algae buildup in the fuel which will clog the filters and possibly the injectors. When equipment is just sitting, certain things will deteriorate regardless of fuel preference. (Mostly rubber parts and seals.)
I recently just did the opposite of what you are considering. I had a Dodge 3500 with a Cummins that I purchased primarily for pulling a heavy trailer. It sat most of the time because it rode rough without a load, and I found that I didn't pull a trailer near as much as I thought I would. It nickeled and dimed me because every time I did use it, it seemed it always needed something.
I traded a Dodge Cummins for an F150 because the cost of maintaining the diesel was higher all around. (More frequent oil changes, higher oil and filter costs, costs for fuel filters, cost for glow plug replacement, two batteries instead of one, license plates, insurance, etc.) The cost of fuel is about 10-20% higher, and any repair parts are quite a bit more expensive when they're needed. I had to plug it in to start it in the winter. To sum it up, it was just plain more expensive and less convenient.
If I read between the lines and you just want an excuse to enjoy the diesel experience, then hey, by all means go for it. But if I were only going to use it to pull a trailer a few times a year (under 5000 miles), I would consider other options.
Dale