I'll throw in, with no offense intended, if you can't afford a bubbler or Ice Eater, owning a houseboat or other boat that size may not be the wisest situation for you.
You might start looking around for old tires or logs to hang all along each side to help relieve ice pressure on the hull.
But additionally , all parts of the engines RW cooling system must be properly winterized, plus the vessel's whole freshwater plumbing system, head , any wash-downs and the like. Plus bilge and bilge pumps including any trap-dips in their discharge hoses.
I read on a houseboat forum steel hulled house boats rust from the inside out so if yours is somewhat older the hull may not resist ice pressure as strongly as a new hull might.
What exactly DO you have for engines and RWC or FWC , and what through hulls are there? And WHERE are you?
Hopefully for you the marina owner does not read this forum .
CWMS- I believe high-mounted heat exchangers on FWC engines are generally pretty safe from freeze damage since the RW side drains down to the W/L. But low-mounted oil and transmission coolers, and fuel coolers and mufflers and low RW hoses and U/W exhaust ports and other hose-associated U/W thru-hulls are certainly vulnerable to freeze damage.
