I would agree with Chris that this is most likely a cost that should be met by IS/JSA.
Although regulation 10 of the HBGR says HB is payable in respect of ‘payments of, or by way of, rent’ (para (1)(a)), which is obviously a pretty broad provision, it also makes specific mention of payments for the site on which a caravan or mobile home stands (para (1)(g)). Common sense (I think) tells me that a tent is not a mobile home in the context of this regulation. Common sense also suggests to me that if the person who drafted the regs went to the trouble of defining site fees for caravans/mobile homes as being eligible for HB, then they would also have included site fees for tents if they had intended them to be eligible.
In addition, past experience tells me that IS/JSA would most probably be prepared to pick up these costs. At my last authority we had a couple of cases (this is about eighteen months ago) where we discoverd that the BA were paying ground rent for claimants at a caravan site – and we were paying the ground rent as well. The BA were adamant that it was their baby and insisted we had got it wrong until we showed them a copy of reg 10.