Fighter Pilot's Breakfast
Dayton, years ago I used to fly sailplanes on the Aleghanie ridges. Much of it was in the cold of winter. In a glider (sorry sailplane) you cant stop for a pee 150 miles from home. At least your friends are not going to thank you for a 300 mile round trip drive, to get you home.
Early in my career it was pointed out to me that what I eat before I flew was crucial. It has a major impact on how quickly you have a problem. I was told a 'Fighter Pilot's' breakfast was what I needed and that meant high protein. So perhaps bacon, eggs and orange. A couple of steaks perhaps as well if that is to your taste. The things to avoid conversly were coffee, corn flakes and pancakes with a good drizzle of maple syrup. They give you a problem
I am not medical so I cant explain, but it certainly works. I remember lasting 7hrs on one occasion, though summer not winter, but up to 13000'. over Altoona.
The alternative is VERY good quality ziplock bags and very smooth air!
WRT the effect on the structure, I once owned a glider made by Pilatus. In very formal english the handbook said if you pissed in the fuselage please wash it out with 7 changes of water!
As far as I can see, otherwise a 3hour trip is just like 3 one hour trips back to back.
Have fun!