I have just installed an elecrtic retract system in my DB Sports and scale Spitfire and they work very well and are very neat and light. No hydraulics or air bottles requred! I bought them from Electron-retracts which is a Spanish company but speak English. The only problem was that at that time they did not supply Oleo legs so I had to get them elsewhere. I understand that the company is now supplying the legs.
Regards
Geoff