I have been running a dehumidifier and a small oil storage heater over the winter And my bill from December to March was £300 ish so I got off lightly.
Most boats can have a holding tank and pump out feature. It might have had a thunder box type toilet fitted before I wouldn't be put off buying a boat without a pompous toilet, they are not that expensive to fit one.
Just been looking at the Potter Bridge heights over the last 7 days . Max height was 5'6" and minimum was 4'9". Something needs to be done as even day boats will pass at these heights let alone Martha's motor boats.
I had the same problem on Nipper I had a stainless one made by the Fabrication Company at Blofield that I cannot remember the name of. I think it was around £80 and took about a week.