I agree with the other replies on here. I don't think it's a good kind of crazy. In the US "class G" is considered "government free" but abroad that distinction doesn't exist. They'll still send you for a tailspin citing you for any possible violation they can think of and could probably seize your aircraft. Remember, general aviation abroad is not a very popular pastime! They will probably find your adventure a bit suspicious and won't take kindly to your low level flying over their beautiful sovereign country. My recommendation is to take your ultralight around the US coast instead. The view of South Beach at 500' is one to remember ;)