there is a new chap making these and selling them at around £100 but he has yet to get specs back to me. he put them up on face ache a while ago but with no specs.
i am sure on them yet myself as never used one but i like the idea and easy to fit but power usgae is needed to be knwn and if it reduces to much cabin heat. a 5WK (8KW) on a small boat can take some loss thugh