Adrianna, are you considering installing a roof basket? I can't remember now if you ruled this out or not. I have one on my 80 and I put jerry cans, water, my highlift, my spare, and other recovery equipment up there with no issues. Yes you want to avoid putting too much weight on the roof but I've tested this setup with mine and run some pretty hairy stuff in Moab with the roof loaded to see how it would react. Yes, there is more side to side movement, but really it wasn't THAT bad and I was doing more technical stuff. For what you are planning I don't think putting some nonvaulables on the roof would be that big of a deal. The advantages that I found are: 1. Not putting a heavy/expensive rear bumper on 2. Hanging alot of weight off of that bumper, 3. The load in the basket can be centered fore aft and side to side better, and 4. you are getting a ton more storage space with the basket.
The only concern I could think of really for you is security of items on the roof and if you really load it down being aware of the handling differences. My 2 cents.
Also, just for perspective, with my 80 I have the 850/863's. Unloaded the rear end sits noticeably higher then the front. When loaded (the last trip I used the truck on was 2 months) it sat perfectly level. I have the stock rear bumper but had quite a bit of equipment with me. I think with what you have planned for mods and the amount of things you are bringing that the 864's might be a better fit (I'm assuming you are going to have a heavier rear load then my uses). Here's a shot were you can see how I fit fuel and water on my roof on my last trip.