Yes, the problem will be the size of an evacuated solar tubes array. Too large to fit on a narrowboat, sadly.
Vandalism, as glass tubes in the reach of teenagers, maybe too much temptation to handle.
PV solar panels on a swivel mounting are more common on boats, so if you have a 120 litres water tank, then maybe a PV heating converter connected to your coil may be an option.
Speak to iBoost manufacturer to see if this is viable, if so, please come back and let us know how you got on with that line of enquiry.
Hope this helps.