What's the collective wisdom regarding mounting a cage under the down tube to carry a fuel bottle? I've seen this done plenty of times but have never had a frame with bottle mounts down there before. My new bikepacking bike will have these mounts and I have a Monkii Cage to use there if required but I keep wondering whether my fuel bottle will be damaged by flying rocks from the front wheel. Any thoughts or experiences? Thanks.

I keep wondering whether my fuel bottle will be damaged by flying rocks from the front wheel.

I'd be very surprised if a plastic bottle got damaged by stones thrown up by the wheel ... aluminium, maybe not so much.

I my mind, it's a sensible place to store fuel - any leakage won't contaminate anything else, it's dead space you probably wouldn't use for anything else and it keeps the weight of fuel nice and low.

Look at the underside of your down tube - how much stone damage is there to the paintwork? That should give you some idea of what you might expect.

Thanks gents. The cage mounts are very low down (just above the bottom bracket really) so hopefully would be clear of most flying rocks. I won't use this option all the time but thought it would be handy for when the extra space is required (I usually carry my fuel bottle in my frame bag). It does seem like a good place in terms of keeping weight low down and fuel clear of other kit in case of leaks. I'll let you know whether any damage occurs in due course.

I've been carrying an mSR fuel bottle there for a while now without any damage
i have kept the fuel pump on the bottle and i was concerned about damaging the pump so Meraid made a hat for it which does a good job of keeping the dirt off.

I've done it quite a lot with no issue.

With a 1.5 litre fuel bottle I hacked up/bodged a cheap torch helmet/bar mount to create a higher strap 'system' above the monkey cage for piece of mind.

Like so:
(Definitely need to T L S! )

Thanks folks. I have various fuel bottles including MSR (alloy) and Trangia (plastic). I'd mainly envisioned using the 500ml Trangia bottle in the Monkii Cage and I may make some sort of cover to protect the spout as suggested by Mpolo. I usually use a recycled contact lens fluid bottle to carry meths on shorter trips and carry it in the frame bag. My new bike will have the option to run the extra cage under the down tube hence the question (assuming that Evans ever manage to get their sh*t together and build the thing so that I can collect it, that's another story though ). Ctznsmith, I have one of those helmet mount things in my toolbox so I could bodge something similar to your set up to carry the bigger bottle, thanks.

Would you not worry about it hitting a rock and exploding?

Cut-off water bottle makes a nice cover for an MSR fuel bottle