I don't know your experience level but the thought of solo rafting a lake that size gives me the chills.
I've been canoeing since elementary school, almost 50 now. Plenty of class 2 and 3 whitewater as well as longer lake and portage trips in the Northwoods. That includes trips of over 80 combined miles of paddling and hiking with gear. I have only minimal experience with inflatables and maybe that colors my opinion. Nonetheless, I would not go out on open water like that in an inflatable for anything but a calm, sunny day laugh.
Any wind will control where you go. Even if you are rowing it will be a battle to go where you want to go unless the wind is in your favor and not blowing too hard.
Maybe you have a lot of open water inflatable experience that contradicts my assessment. However, if you don't have that experience and you just want to try this trip and know that hauling an appropriate boat over a glacier is beyond your abilities then consider that a raft is not optimal for any sort of long distance, open water crossing that isn't intentionally wind powered...bringing up the question of sailing experience and equipment that would have to be hauled over the ice.
I don't look forward to reading about the search for your body a week after the raft was found.
