So, answer the OP's question:

How do you make a reservation in a secure manner with any BVI entity you would like to deal with?

(1) email and ask for a CC authorization form, fill it out and send it back by the easiest means for you.

(2) phone call.

Caveats: you may not always get a response via an email inquiry. fall back: call. If you're going to call see the multiple options for doing that at a reasonable cost above.

I have ATT so, I'm not going to change providers to access better deals. If you are going to get an international plan (ATT Passport for example), you have to assess the value of that compared to the cost of just making one or two phone calla and getting charged for it on a by minute basis. It can be quite expensive that way.

My preference is to use email if I'm making reservation more than a month out then add the ATT PassPort plan that will cover a period both 2-3 weeks before your charter and the charter itself.

Last trip I bought the Passport plan on July 3rd for a charter that went from 7/16 - through 8/2. I made several calls/texts to verify orders before the charter(Caribbean Cellars, DeDe's Car Rental), a couple of local calls while on charter and paid $60 for the voice/data service. I rang up $25 for calls over the 30d period.

You seem to have legitimate concerns about CC Security. If you don't have one, get a Capital One credit card then set it up for alerts. It's the only CC I use when I travel but I carry an extra one (USAA MC) in case I have to freeze my Cap One card. Every time my Cap One card was charged, I got a text alert. I had one unauthorized charge early in the trip, noticed it right away, phoned the CSR at an 800 number and it was removed. It happens. I don't care how security conscious you are. Be prepared for it with approaches like this one.

I also have a travel debit card account with PNC bank. It's not attached to any other bank accounts to prevent misuse (e.g., all my accounts getting drained). I put $250 into it to start and go from there. I use it mostly to get cash if needed but will also use it for payment for goods and services. If I need more cash, I move it on a secure connection via my bank's web site.

Speaking of ATMs outside of RT. IMO, there is only one safe one (others may offer other safe ATMs). Its in Scotia Bank in Spanish town. It's a block from the Harbor and has an ATM both inside the bank (accessible during normal banking hours) and outside (accessible all the time).