We purchased a portable unit from Target several months ago. The brand name is Magic Chef
and it sold for approx $150.00.
They will not keep the ice froze so if you don't use it right away the ice will melt. We make large amounts then put it in the freezer
for future use. We have run it off the inverter
several times with no problems and it does not seem to put much of a drain on the battery
My complaints are even though they say compact they are quite large so finding a spot for it is a pain. We have to secure it before getting under way which is also a pain. The other problem is the obvious that it does not keep ice frozen.
From what I understand the built in units will keep ice frozen and when you do the measuring they do not take up much more space than the portable unit.
Personally I am keeping my eyes open for a nice built in unit.