I am keen to order a VIDA - FUSION 1200 STEAM 120cm X 90cm. The space between the walls is 140cm so it will fit, but I see on your site that you state there needs to be 40cm gap to access the unit should repairs be necessary. Is it essential to have 40cm or is that a recommendation. What problems will I experience if I only have 20cm gap? Please advise.

The space required is simply enough to be able to get a person behind the unit. This is required for the build as the items are built from the outside rather than the inside so access is required to fix the panels and hoses, fittings etc. 

The manufacturer then recommends the showers are not blocked just in the unlikely case you need to get access again

The golden rule is, you need enough space down one side and at the front/back to allow a person to stand and get access