If this doesn't work out for you, you can always go with a
regular private home rental. For many people, Tortola is only a part-time home;
they spend much of the rest of their year in the U.S. or in Europe. When they're
not around, their homes are rented out by caretakers. These homes are often
inland, but in a few cases you'll find them right on the beach. Shop around for
the best location and the best deal, and don't be afraid to negotiate,
especially in the off-season and especially if the home is rented directly from
the owner and not through an intermediary.
You also have the option of staying at a resort or hotel. Resorts on Tortola are only all-inclusive if you opt for one of the American plans, which cost more but add meals and more. Hotels do not typically have that option. They are also few and far between on Tortola. More people stay in the hotel-like accommodations at marinas than stay in regular hotels. If you want a hotel, you are almost certainly going to be staying in Road Town; if you want to hit the best beaches, you'll need to drive or catch transportation out to a different part of the island, probably at least 20 minutes away.
Finally, you may be able to camp when you stay on Tortola. Camping on public land is not legal, and the only real campsite you'll find is at Brewer's Bay. You may, however, be able to locate an uninhabited island that you can pitch a tent on. If this is the route you take, make sure you pitch your tent at high tide!
One other option for a place to stay in Tortola: if you're going yachting or doing some serious boating, you'll be able to stay in your cabin for the duration. Plan this into your itinerary if you are going to do an overnight trip on the high seas.