Grapes in a polytunnel

can I ask if anyone has any experience of growing grapes in a polytunnel. I thought about using the back bed which is 30 foot long by 4 foot wide, good depth and good soil and would appreciate advice on varieties and spacing -- could we get three types in a 30 foot length??. We are seeking eating grapes (rather than making wine) with a spread across the cropping season. Location is a sunny well sheltered garden in north lincolnshire. Close to home for watering and attention and security luckily.
many thanks
R

I have a grapevine which has its roots in the ground and the top inside the greenside, which I've trained to go along the top of the greenhouse.  However, one thing you don't do with grapevines is don't water and don't feed.  If you do, all the goodness goes into the leaf, this is ok if you wish to make stuffed vineleaf recipes, as you won't get much if any grapes.  They are forced to find their own water and feed, so they actually put the growth in the grapes.  I've learnt this from various grapevine growers in France.  When you drive through wine country, notice how all the vines are always on the sides of hills, this is for the water to drain down and not water log the vines.