8000 lbs dry or wet? For my 5th wheel, that is almost 5,000 lbs different from dry to max weight. What brand? Those fiberglass units from Canada, I think they are called Carefree, are even lighter than 8000 lbs.
I've seen it done, with 5th wheels made for half tons. The axles are much farther apart than normal, over a foot. Mine are like two inches. This is like that lighten up the pin weight, where you're going to need to watch the weight there. I saw one and it looked scary.
I knew I was going to go to a 5th wheel, I stepped up to a '21 Ram 2500 6.7 L Cummins diesel added some air bags to the truck (something else for you to consider adding), and hit the road. You'll need the bags for sure.
And watch your engine oil temperatures in the hotter sun areas.
Also don't forget the weight of the 5th wheel hitch receiver and hardware under the bed.
Good luck and be safe.