My man told me a while back never to install an RSD wider than 4 metres. The middle one of the three we have just installed above (March 2019) is 6 metres wide. But it is an internal rather than external door so it should have a lot less exposure to rain and wind. Plus it will only open and close once a day. Fingers crossed.

Unless you are on the edge of destitution, install one with an electric motor. They are very reliable and if it does break, easy to get at (unlike anything underground)

You DEFINITELY need an alternative entrance eg via a fire door because one day the RSD will stop working. Usually a power failure or a breaker tripped. Obviously, if it is a manual door you do not even have the option of opening it from the outside so you always need another way into the building.

But do NOT install one with a wicket gate in the RSD unless it is absolutely unavoidable - they are nothing but trouble

If you are isolated or vulnerable to break-ins, a couple of massive steel uprights that drop into holes in front of the RSD by hand are well worth the trouble to stop ram raiders and reversing lorries. They will help you sleep at night. Don't go for hydraulic or electric - they are very unreliable and when they fail underground you have to dig for victory (see Bollards above). Just get a local guy to make them from old railway lines or really solid RSJs. Don't skimp. Make it so heavy and solid that you can only just lift them with two people.

Or get a huge concrete block (or rock) on a pallet and sit it outside the RSD at night with your fork lift truck. As big and heavy as the fork lift will handle.