It rather depends.
You can DIY by buying a length of relevant type of hose from an Eriba dealer, or probably any caravan dealer or accessory shop. If it's damaged at one point it could even be a very short piece and join it all together with link inserts and jubilee clips.
I'm not sure if Hymer sell a prepared replacement, but if they do, it will be costly and only available via a Hymer appointed Eriba dealership.
I'd suggest discussing with Kool Classics as they know what they're talking about on such things. The other dealers, not so much.