When you say The Gatehouse, do you mean the Railway Gatehouse just down the road?

According to the Manx National Heritage Leaflet 'Sources for Family History' there are voters lists held at the Manx Museum for 1919/1920 (archive Ref: MS 09842) These are not online.

If you want to pay me to look them up for you contact me at david(dot)radcliffe(at)manx(dot)net