Prior to leaving, I also borrowed a Bluechart SD card for the area and loaded into my Oregon 400c (thanks Frank!), which proved to be extremely useful. I quickly fell into my normal routine of plotting the next day's planned route on my laptop in the cabin (using OpenCPN with the NGA charts that I had calibrated for digital use), then using MapSource to transfer the routes to my Oregon for use in the cockpit. I installed the Oregon handlebar mount at the starboard wheel so I had the route available in the cockpit at all times.
I need to say that I consider the availability of pre-plotted routes to be a critical safety item when navigating unfamiliar waters. No matter how good your ded recking skills may be, when you look out along the hazy horizon in a place like BVI, it is impossible to tell whether a certain feature in the distance is a cove, a bay, or a cut between islands.
Also, the more robust sailing in BVI caused more water in the cockpit than I was comfortable with the iPad.
The last statement of the quote (which I've condensed) is why I would not consider a non-marinized chartplotter for my helm. Anything will work when the seas are calm and it's not raining. But when that squall comes along while you are in tight quarters, you want something in the cockpit that is rugged and waterproof.
When you are going on a charter, you don't necessarily end up with the installed equipment you'd like to have. Bringing your own portable equipment with preplanned routes will surely add to your peace of mind when you are away from home waters, but you want something that can stay with you at the helm when the going gets tough.
I also have a Garmin Oregon and have used it in the Virgins as my primary piece of navigation gear. However, I programmed the routes (primary and alternates) directly on the Oregon before leaving home, after consulting the guides and my own waterproof charts. Programming your routes on the device you'll have at the helm will minimize confusion when it matters. The only other electronics I bring on a charter is a cell phone.
BTW, I bring my own waterproof charts--typically Imray-Iolare--on Caribbean charters and rely on them to keep the small Garmin screen in context. They are also a familiar backup for dead reckoning, should the batteries run out or the electronics fail. I also bring detailed chartlets for certain areas, like the approach to Anegada or Christiansted (St. Croix) to augment the larger charts when necessary.