We used to own a static caravan. The sight was lovely but did not allow sub-letting to anyone, so please check that out first. Also, after a couple of years f going to the same place for our weekends and holidays, it got very boring, even though we actually loved the area.
Also, we had to do all of our own maintenance on the van and the pitch it stood on. The site owners only maintained the communal areas, so check that out too. They insisted the thing was washed down at the beginning of each season, for example. It was a pain.
Our friends used to own one which was on a site which allowed rentals, but they had to do all the turnarounds themselves. They live in Birmingham and the van was in South Wales, so they literally had to go there every weekend over the summer. It wiped out any profit the made.
Some sites have an age limit on vans too ... they don't want old ones making the place look run down, so you may not be able to keep it long enough to re-coup and investment. Another question to ask ....
When we sold, we had to sell back to the site (a lot of sites stipulate this), and, whilst they made us a reasonable offer which we accepted, they then sold it back on to another buyer for over £3k more ... another thing to consider.
Really OP - all things considered I'd think of another way to invest your windfall, as the caravan idea has too many pitfalls.