I have one in Aberdovey, it's been in the family for years (not the same van).
It does cost a bit to keep it on site, around £1350 a year ground rent, £250 a year for insurance and £100 a year for electricity and around the same for water. Some sites include electric and water in the ground rent, check before signing. Gas bottles are 60 quid a pop. We get through around 2 a year. The biggest expense was the van itself. I bought it in 2017 and it cost £36k
Now our children are grown up we don't use it for our main summer holiday, instead we let family members with children go in July and August. We go for long weekends from March up until October and weeks at Easter, Whitsun and September.
Pitfalls? Obviously you'll be spending a lot of time and holidays in the same place. Make sure there's enough for you to do in the area. Look out for additional fees on top of the ground rent. I know sites which will charge for grounds up keep, grass cutting, as well as road and building maintenance.