I don't agree with some of the points you raised above:
1. Low barrier to entry. I don't think that this is the case. For a new entrant to become a serious competitor to THL in their core business of hiring full size self-contained campers, there are considerable barriers to entry. It will take quite a bit of capital because these are not cheap vehicles. It is not easy to find suitable locations close to the major airports. There are airport licencing requirements, although these are a relatively minor obstacle. Much of the business comes from wholesale travel agents with whom THL has a long standing relationship. It would not be a trivial task to go to Europe and convince these agents to switch to a new operator, and even if successful there would be a fairly long lead time required. Although a new competitor could probably make better inroads in direct sales, via internet.
2. Competition from vans they are selling off. The reason they are selling off these old vans is essentially that they are no longer fit for purpose. If a competitor is buying these and they are STARTING on their fleet at that point, then they are really operating in a different market segment altogether. THL's real competitors, like Apollo and Jucy, use newly fitted out campers (Apollo does their own fit out). A holiday in a self contained, reliable (not too old) camper is not a cheap option. Sure, some tourists will not recognize that you get what you pay for and will figure they can have the same holiday in a clapped out old camper at half the price. But usually the result of that is that half the holiday is ruined by various equipment breakdowns and other problems.
IMO, the challenge for THL is that a proper, decent, holiday in a camper is competing with a cheaper rental car/motel/B&B alternative. Now these are two quite different holidays, but how much more are customers prepared to pay for the camper experience? It seems to me that THL has had to price the campers too cheaply to make an economic return on assets. Can they streamline their business to make an economic return at the prices that customers are willing to pay for the experience? That's the challenge. Everyone in the industry has gone through a few lean years in both NZ and Australia, some companies haven't survived at all and some have been bought out by THL. But times are improving and THL seems to be getting it's act together.