We wish you all a Merry Christmas, Happy Holidays, and fun travel dreams!
I know nothing about Grande Isle. We did stay in Bayou Segnette SP. It is an excellent location to use as home base when touring New Orleans, World War II Museum, & Barataria Preserve. Nice level sites, free laundry, and half price camping with the NPS/Interagency Senior pass. Don't know if all Louisiana state parks discount.
I highly recommend you eat your way through Louisiana! Meat pies in Nagadoches - Boudin Balls and gumbo and jambalaya in Cajun country - and so much more.