I may be wrong, but here is my take. Remember, advice on the web may just be worth what you paid for it ;-)
The 811 was the shortest Lance camper with a slideout at the time, with a floor length of just 8'6".
Technically, it should fit on either long or short bed trucks; my preference would be a long bed. The sales brochure doesn't seem to specify the required bed size.
But it says that they are proud of the low profile of these campers. I am not sure if they even have a basement. From the pictures I have looked at, I think not. Somebody please correct me if I am wrong.
Lance gives you access to historic brochures and manuals; go and look for yourself:
https://www.lancecamper.com/ -> Owner Support