I have a 31 with a Force 10 Cozy Cabin LPG heater installed on the port side of the forward bulkhead. I didn't install it but I am very happy with it--it's simple to use, compact,sturdily built of brass and stainless steel and heats my 31 easily. Rated at 6000BTU and looks like they're selling for about $400. I realize there is a lot more volume to heat inside a 37 than a 31, but there's my $.02 anyway.
PSC31 #9 "Wayfarer"
The secret to sailing is good judgment. Good judgment comes from experience. Experience comes from bad judgment.