Hi John.
I have a 2005 Abbey freestyle which is a product of the swift group. We had the shower tray crack just in front of the loo an the ridged tray floor. A few days prior to finding the crack we found our shower tray floor to be spongy. There was also some creeking. As our van was out of warrantee I decided to have a look myself and try to fix the problem.
On removal of the shower tray after dismantling most of the toilet room, as all the other fittings were located ontop of the tray etc. I first of all noticed that the piece of foam insulation board had deteriorated and was compressed slightly, thus giving the spongyness. Also I noticed that the ridges of the floor where the most foot pressure is placed were hollow and as such would of been offered no support by the foam board unti it had fully degraded into the profile of the floor. As the foam board is not designed to mould to the tray shape, it would take some time before it would sink to the shape.
To repair the tray I did the following.
First of all I fibre glassed the cracked area on the underside.
Then I filled all the hollows of the ridges with a good quality bathroom type silicon sealant.
Make sure you do this in a well venitated area as the fumes from two tubes of sealant used to smother the whole of the bottom of the tray become very punjent.
I then did a simlar skim over the surface of the foam and then fitted the foan back onto the tray.
Now all that is left is to refit the whole of the compartment with the parts you took out and seal the whole lot up.
The job take a couple of days and is realy only suited to a very competent DIYer or a proffessional engineer.
I can honestly say that my tray has repaired well and you realy have to know where the cracks were before repair to actually find the repair and even then you need to be on your hands and knees to find it.
I saved over