Bailey end panels are vacuum formed in acrylic capped ABS.
I had 30 years experience in the industry and predicted this problem with cracking some time ago in this forum.
There are three main causes:
1) Vibration around fixing points.Unlikely in a caravan but possible.I once supplied a new customer with a cover for a compressor which stress fractured around the fixing bolts in a few hours use due to the vibration of the single cylinder engine.
2)ABS absorbs chemicals,and once it has done so tends to go brittle and crack.It especially dislikes aromatic chemicals such as white spirit,ammonia,alcohols etc.Clean your caravan ends with an aggressive fluid and it will eventually crack.It is not always obvious what is in a domestic product:my wife took out three ABS shower control unit covers with Flash.All three cracked around the hidden fixings.
3) UV degradation.Ordinary ABS loses half its impact strength in 6 months UV exposure.Acrylic capped is much better as the acrylic
capping acts as a filter,but even this will eventually degrade
(probably outside the six year warranty).
I suspect the cleaning fluid used is the culprit,as this explains why one persons caravan cracks and the next persons identical model does not.
There is some confusion out there as some earlier caravans (eg Abbey) originally used fibre glass panels,which are a totally different material.On the outside these panels look identical,however inside they will have either a woven pattern or a chopped strand look.ABS panels are totally smooth inside and out.The only true repair for an ABS panel is total replacement as there is only a mechanical bond between filler and panel and this will eventually fail.Also if the ABS is brittle in one place due to absorption,then other areas will be the same and waiting for their turn to fail.
On my Vendee I used plain water to clean,and Mer polish to give a shine and take out stains as this stated it was suitable for caravan use,and I had no trouble in the four years I had it.