if you are working with a local contractor, use them find someone on-island to arrange work permits. They may have someone dedicated to just that. The logistics of that all really is a full-time job, but the benefit is that everything should be above-board so you can go through customs fairly quickly and take your tools down and back as needed.

Shipping can add days, weeks, or months. One time we had advance replacement parts shipped from manufacturer that arrived in two days. But other times we wouldn't even book travel until getting confirmation from contractor that shipments had arrived. Again, send as much possible utilizing an on-island contact / through GC.

The other way is to just fly in without the advance work and take your chances. But the customs guys are good at their job. If you don't have enough extra cash for them, they are usually kind enough to drive you to a local ATM.