I have 2 dogs, a dobe and a Terrier X who sleep in the conservatory which has central heating and is as warm as the rest of the house.  Both have been house trained since about 5 months old.  But recently we bought a big thick plastic inside dog kennel for them to sleep in as I thought there was a draught in the conservatory and thought it would be more cosy for them.  They absolutely love it but one of them is peeing up the side of it, on the same corner.  I have never seen them do it and I think its the Dobe as he pees up everything plastic in the garden, whereas the terrier goes up bushes.  Its not a lot of wee, so I think it is more a marking his territory rather than needing to go. 
Any ideas how to stop this, Its no use telling him off because he hasnt done it when anyone is about.  Is there something I can spray on it to stop him doing this.

Luckily the floor is tiles so it cleans up ok but the husband wants to get rid of the kennel

Would he pee on it if you covered it with a blanket? Of course after you cleaned it up real good so he doesn't smell where he last marked..

Try washing with Bicarbonate of soda, then covering it over? He might still do it if he's 'marking' anyway!! LOL