Jack,
I purchased the Espar through a company called cool-it in Canada. Link below.
http://www.cool-it.ca/ShoppingCart/.
They had a listing on Ebay for the Espar hydronic kit (18,000BTU). Included eveything except the through hole fitting, and the radiator's. I just checked Ebay and they have one listed for under $1200.00. Excellent service, we received the unit from Canada in 4 days. We also checked locally for the Espar and were quoted $2500-3500 for just the parts, $6000-7000 installed. We also heard we needed an additional pump, our system does not have one and functions fine. You will probably hear that the higher priced unit is designed for the marine environment, and the cheaper units are truck heaters. I checked the part numbers the heaters are same.
The 2 radiators I ordered locally from MSR marine. Call Jim at 206-546-5670. they were 135.00 each. He was also helpful in picking the right size heaters for the Catalina 34.
He recommended two smaller radiators, and he suggested we install them at the far ends of the main cabin. We did not plumb any heat into the cabins, as we like cooler sleeping. Through hole, plumbing and fittings added another $250-300.
The install was straight forward, and would not hesitate installing the Hydronic again. We spend alot of time on the hook and the wife wanted hot water. The radiator's have a 2 speed fan and on low they are verrrrry quiet.
I hope to be at the Catalina 34 get together next weekend, if you are coming maybe we can talk further.