There's certainly nothing self-evident about how true lockean and neo-lockean property would actually work. In the homesteading model, "something" of the person is "mixed" with unowned resources, which annexes those resources to the person. Neo-lockeans throw up their hands because they can't make practical heads or tails of the "enough and as good" proviso (and generally ignore the proviso against waste), but, arguably, the provisos are a lot clearer and more clearly practicable than the mechanism of appropriation. Of course, neo-lockeans don't focus on appropriation anyway, skipping ahead from the "state of nature" to the exchange economy, where division of labor and exchange will have effects virtually "as good" as proviso-appropriation. But, yikes! If the original standard was impracticable, then how hard to practice is its virtual equivalent? Rather than basing itself on a principle that's about as close to self-evidently universal as you're going to get—and then confronting the problems of applying the principle—neo-lockean property simply abandons the principle, and asserts that which is far from self-evident: that an exchange economy in which the appropriation rights of others are simply not considered will have virtually the same effect as one in which appropriation is direct and guided by the provisos. Seems like an easy way to go astray. And, sure enough, true lockean property is virtually non-rivalrous (and amenable, at least in principle, to adjustment to account for long-term sustainability and ecological effects, for which "good fences" are hardly a solution), while neo-lockean property is rivalrous by definition, and inflexible (mostly unconcerned, really) with regard to the material, systemic complexities of actual property in the real world.
Compared to all of that, how difficult a principle is "occupancy and use"? Take the lockean provisos seriously, and add the fact that natural processes "unmix" all the while—observe that anything in perpetuity is about as un-natural a principle as you can imagine—and you can derive it from the same roots as neo-lockean theory, with less opportunistic reasoning and jimmying of the basics.
The straw-man depictions from propertarians probably reflect a basic difference in political aims and cultures. Mutualists are not occupancyandusitarians: our theory of real property comes a couple of steps after our account of "self-ownership" or "property in person," and it is certainly not prior to the principle of reciprocity. You could, no doubt, construct a mutualist account in which "all rights are property rights," but the "property" certainly wouldn't have the exclusive, perpetual character of most propertarian systems. From a propertarian perspective, the notion that property isn't forever—or isn't at least dependent on the intentions, however inert, of the proprietor—seems outrageous, so there really isn't that much difference between moving into your house when you nipped out for a carton of milk and opening the land of some distant holding company to occupation by the landless. Having jettisoned the provisos, and no longer being able to fall back on the actual homesteading mechanism (the effects of which market exchange is supposed to approximate), neo-lockean theory doesn't have a lot of guidelines to fall back on, so it makes a virtue of being "tough, but fair." If you question the "universal right of first-come, first-served" stuff, chances are the propertarian isn't even going to see a problem.
Anyway, apart from any mutualist reimagination of property, possessory occupancy and use conventions are going to be based on the principle of reciprocity. When propertarians insist that without their form of property, mutualists will "steal" anything that nailed down, my first question has to be: Dude? Is that the way you imagine the Golden Rule playing out?