Hills make the route selection a little tougher, of course, depending on how you handle hills on the fg. I tried it once but didn't finish it, though not because I couldn't have (crashed out at 50 miles because of a dumb move by another rider).
I don't think there's anything special about preparation, other than trying to get terrain that you can manage on the fg. Compared to a century on a multi-geared bike, you can expect your legs to be more fatigued before the end. Food and water stops need to be planned. In your climate, I don't think you can carry enough water to go the whole way.
I've done a few metric centuries on fixed gear bikes, one was setup 48x17t, the other one is at 48x16t. First time around the legs felt different compared to how I feel after a road hammerfest. More generally worn out yet less muscle fatigue is how I can best describe it.
Bring lots of water and eat adequately. Stop as frequently as needed. Pick routes that you know well.
I did an charity MS-150 (75 miles x 2 days = 150 miles) fixed, nothing special for training. It was fairly flat - but I'd think as long as you had the right gearing for hills you shouldn't have any problem.
Done it a couple times, though the hills were more "rollers" than all out extended climbing. No special prep needed, just make sure you're comfy on your bike for ~5 hours. If there's lots of climbing involved gear selection will definitely be a factor. You can find a gear that works great for climbing or descending, but not both, so either split the difference or be prepared to grind on the uphills (or spin like crazy on the descents). If the descents are switchback types I wouldn't even bother...not real safe.
I rode the Farm to Fork fondo in Lancaster PA yesterday on my fixed gear. Ride Details & Prices ? Farm to Fork Fondo
It was a challenge since it had 6700' of climbing and a couple of bits where the grade was 10%. I was very tired when it was over. The food and support were fantastic. I would recommend any of the farm to fork events.
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