I live in a 30 foot static. I was brought up in one. I've lived in this one for a few years now.
It can get a bit exciting in the wind, but the hitch end is pinned down by a buried sleeper, and the other end has an iron rod hit into the ground at an angle.
The first morning it froze, I woke up, and may as well have slept outside for all the difference to temperature the static made.
Now it has two inches of insulation in the walls, covered over with hardboard, and nicely decorated. I covered over most the windows.
Four inches in the ceiling, and oil powered central heating. All fitted by me. I also have a woodburner, but it's pretty useless. Come home at night, and be the time the place is warm, it's bed time. It won't keep warm overnight. It's not even worth lighting it in the morning. By the time it gets going, I'm off down the road.
Shop around for stuff. Insulation can be had cheaply. My mate has just dropped off another fully functioning central heating boiler, for nothing. They are being scrapped all the time.
Rats have always been a problem, much more so than a house. Strategically place traps are a help.
If you've got running water, get all the pipes inside, they are often run outside, and will freeze in winter. Putting a bit of lagging around them is not a solution.
I fibreglassed straight across the top of my skylights. They are a waste of time, IMO.