The first question is as to whether the site comprises "premises"
""2) Subject to the preceding paragraph of this article,( ie the exceptions domestic, woods and fields etc ) this Order applies in relation to any premises.""
I am not sure of the legal definition of premises so to tie it up further - is the site a workplace? If it is- if someone is employed to maintain clean or service the site - then it clearly comes under the FSO2005.
The relevant persons are any persons who has legal right to be there and the risk assessment needs to be recorded because a licence is in force.
The FSO 2005 modified the Caravan sites Act to the effect that if ithe site is a workplace the fire safety requirements will be imposed under the FSO and Not the Caravan sites Act.
But I guess the safety standards applied will be the same re spacing of units, provision of fire points etc irrespective of which legislation has effect.