Here's the problem - chopped strand mat doesn't like to go round 90 degree angles which is why it's often recommended to form a radiused corner for it to go over rather than a right-angled one wherever possible. The reason is that the mat is made, as its name implies, from a random layer of chopped glassfibre strands which are temporarily bonded together with an emulsion.
(I don't know what "an emulsion" means, I just read that.) This holds the mat together but also makes it resistant to bending until it is saturated. If you fold the dry mat and run your hand along it it will bend but it won't crease and it won't hold the fold. When the mat is laid on wet resin and saturated with more resin, the emulsion is dissolved and the glassfibre strands are left suspended in the resin which is what gives the resulting composite its strength. At that point, until the resin cures, the mat is quite flexible but it's also impossible to move.
On my camper the the small vertical 'stand' around the hole in the roof is what's going to keep the rain out and the inside dry so I had to be able to glassfibre it but I really didn't want a radiused corner between that and the flat of the roof. Or, at least, I wanted the radius to be as near zero as possible. So somehow I had to find a way of getting the dry mat to hold a crease.
Here's the answer - treat the mat like any other fabric and iron it. I didn't know whether or not this would work but it seemed to me there was little to lose and so I went in search of an iron. And kudos to me for knowing that we still had one somewhere at the back of the kitchen cupboard. Clare (Mrs saDgit) thought we'd got rid of it years ago. Mind you it doesn't get used much. We bought our place in France 11 years ago and the iron's still got a UK plug on it! We figure that if we stand out because our clothes aren't ironed we've probably gone to the wrong place.
Anyway I discovered that by folding the mat over and then ironing along the crease, just with the edge of the iron, the emulsion disappears (presumably melts?), the fibres soften and the crease holds. So I was able to make lengths of dry, angled mat ready to lay into the corners once I'd brushed resin onto them.
And it worked a treat.
I've only done this with a dry iron and it worked well. I don't know if you sprayed the mat first with water, or even used steam, whether it would be better, worse or the same. I doubt whether the temperature of the iron is critical but the 'cotton' setting worked for me. You do have to remember that, because the emulsion has gone from along the crease, the mat is weaker there and has to be handled with care. On the plus side, because the emusion has gone from along the crease, the fibres are softer and will soak up the resin much more willingly and so it's easy to push the mat right into the corner.
I don't think the process left any residue on the iron but if your silk shirt ends up stiffer than usual, or your wife's dress sparkles with tiny shards of glassfibre, I'm afraid you're on your own!
. So while I've been waiting I've glued the front and luton floor panels in place, holding them with a kind of Heath Robinson combination of clamps, blocks and ratchet straps while the glue cures.
Shame I didn't go for that sliding canopy as well though! Although I'm not sure that it's demountable (at least not in this model), hanging the kitchen on the back door under the canopy (Australian camper style) leaves loads of layout options in the camper body. I like it! Better start again. 
