Hello, yes they do, both Webasto and Eberspacher. the Webasto Thermo Top E (4kw) is still available, but only just; it'll soon be discontinued. Webasto UK hold stock of the heater but we ourselves would need to assemble the ancillary items for marine application in this case. That's no problem, we hold everything in stock to do this
Also the new model Eberspacher S3 is now available to order as a Narrowboat kit with a reduced output of approx 4kw - delivery is 2-3 weeks from Eberspacher UK. Pricing is similar to the 5kw heaters.
Thank you for enquiring