DEET also has a MG issue. It is an acetylcholinesterase inhibitor, just as Mestinon is. Skin is porous and that can act on your body the same as Mestinon. Too much of a CI and one can have a cholinergic crisis. Hey, maybe that and the heat will cancel each other out!
DR can be a very interesting place. But you will probably need to say no to some activities. I loved the trip to Santo Domingo, but it was a very long one. No AC in the bus.
Maybe you can call the hotel and find out about netting. And then there's the flight over the Bermuda Triangle! Kidding!!!! I'm sure you'll be fine. I gave you the address of the medical center close to where you are staying. You may want to see if they have experience with MG.
I am doing my best, given the vortex of difficulties lately. Thanks for asking!

Annie