I would call Volunteer Landing and Louisville Landing about rental house boats. I have done Vol Navy 2-3 times a season for years and it is something to do once in your life and more if you can! We will be docking for the OK game Friday afternoon till Sunday!
I remember a houseboat being parked behind us last year at one game, I think it was the Utah State game, that was rented. The marina brought it up, parked it and had it set up for them. Not sure about the cost.
I would stay away from Ft Loudon Marina. That's where I keep my boat and it is almost exactly 50 nautical miles to the Stadium by river and in my boat (34' Sea Ray Sundancer) we use about 225 gallons of gas on the round trip total. You will need at least that size boat or larger for a party of your size and if you plan to spend the night which I recommend (more fun after the game than any other time imo) you will need a houseboat. Great marina and people at FT Loudon just not the best place to rent a boat for Vol Navy imo. A Pontoon from Ft Loudon to the stadium would be a rough ride with all the 50' boats throwing 5 and 6 foot+ wakes.