What's the best thing......

........to use as a letterbox container?? I see a lot of icecream tubs/plastic containers and sometimes pill pots but what is the best thing to use? The most waterproof thing I assume would be best so is there a type of box/pot that works best or even a brand that leaks less/can cope with freezing temps? Is plastic the best option? Where do you even get those big pill pots from???
Just wondering about this as I've found so many leaking boxes (perhaps the siting of the box is the biggest factor/ the way people put the box back?) and I'm hoping we will put or first box out next year.
Any tips on avoiding water logged boxes? or is it unavoidable?
Thanks!

The location of the box is all important - under a gorse bush, flap of turf or any vegetation and it may get waterlogged. Under a rock seems best, but ensure the rock is not in a location like a hollow as that can become flooded after heavy rains!
Seen all sorts of containers over the years - I reckon the best were the pill pots. Unfortunately they are very hard to come by now unless you go to a company that sells them 'bulk buy' Local chemists used to provide them free but they no longer have them.
Plastic containers are generally used and the best I think are those 'clip lock' ones but tend to be expensive so you need to look out for 'offers'. There are others such as 'Tupperware and the branded ones in supermarkets (Buyology and Morrisons often have offers of 'Lock Lock'). Problem is - getting the boxers to 'click' the lids back on tightly! Seems once the stamping has been done it is getting more often that the box replacing is somewhat haphazard.

TWA

The clip-top (kliplock? klipfresh?) seem to be most favoured, and are very waterproof - but if exposed to sunlight become brittle like most things.

On the pill pots - coming across quite a few now that are similarly brittle and leaking, but they've done well. I'd be leaking if I was left out on the moor for years.

Ammo box still king though, but expensive to get at the military have asked they're not used in firing ranges.

Totally agree about siting when possible. Out of sun as well as water.

DNPA requested a few years back that Ammo boxes were not be used as the army types do sometimes forget to remove theirs, but I found if the box is painted another colour some of the peope will turn a blind eye. But as you say - they are hard to get hold of. Some years back I went to Chelson Meadow and came across thousands of them, sadly I wasn't allowed take any of them.

The plastic pill pot was brilliant but subject to lazy boxers not putting them back correctly and dropping the "guard stones" and breaking the things.
So now we are down to the locking type boxes which also suffer the same predicament, lazy boxers.

One day... the perfect container will come along

Thanks for all the input, clip lock box it is then.
Are guard stones rocks put in front the box to make them less obvious?