Hello Barny,
How come I don't know you already? I'm an ex-Kenyan, currently freezing in France, I am sure you know Eric H?
Anyway, a gimbal is a gimbal, whether for MR or SR use, and wind/weather protection is not really that essential. If it is not completely airtight - and I don't know of any that are - it will just get dusty inside and be more difficult to clean the camera etc. Gimbals were being mounted on heli's long before multi-rotors were dreamed up so it is not really a new challenge, other than tackling the different vibration on a single rotor heli if you come from the MR world.
You will face the basic choice of front-mounted or underslung camera mount/gimbal. Front-mounted keeps the heli CofG closer to the rotorhead and tailboom line but invariably necessitates counter-balance weights on the tail boom, unless things are changed around. If it is to be an electric SR heli then the main power batteries are very useful for counter-balance use as you are not adding any more weight than would have to be carried anyway. Actually mounting the camera mount to the heli is more involved as some sort of support has to be fashioned for it to hang from. This support has to sturdy but also vibration isolated. THAT is your main challenge.
Underslung is usually a self contained frame containing your 2 or 3 axis gimbal and all related batteries, gyros/stablisation, downlink etc. slung from the skids with foam tubes and bungie. This method can offer unrestricted 360° pan, whereas a front-mount is limited by the heli frame behind and skids below. However, it can also de-stabilise your whole rig and needs to be substantial enough for a few 'bumpy' landings. One more thing. The Pan axis. People tend to go a bit crazy when they have a Pan axis to play with. It is so easy to over-use it with the camera darting left and right. It does not make for satisfying viewing and should be used only to make a point with a specific subject. Your most useful axis is Tilt, given that the Roll axis should just be left alone to hold the horizontal, and by enlarge the camera should be left to record what it sees without constant movement.
