We see you have been a member for a while now, nice to hear from you.
Firstly what Dandy do you have?
Is it the bed bases or the bed ends you want to replace?
We have replaced both bed ends and one bed base on our 6 Dylan and as Navver said it is just a case of drilling out the rivets putting in or on a new piece of ply and re-riveting. When we replaced the bed base we cut the ply square and by doing so had to put new metal straps on underneath as we had squared the bed base up and they where 1/2" short. This is a typical Dandy quirk if you do bits to them you will find out.
If yours like Phoenix our 4 berth you may have wooden framed bed bases which will need a different approach.
Here is a link to what we did, must admit it took a while to find.[You must be registered and logged in to see this link.]