Just had a look at the MK info.
This wont do it, the Masterseal uses specific switches, not the regular grids and MK dont do intermediate for that range.
A moments work on google (go on, try it sometime) revealed that Hamilton do an intermediate IP55. See
http://www.hamilton-litestat.com/pdfs/Weatherproof.pdf
You should be able to order from a decent wholesaler.