idaho is bill of sale and you list selling price on title. this establishes tax liability. I have sold a lot of newer cars for $1000

not sure on Wisconsin as I have not bought a boat here but if it's like car, it's based on price on title.

trailer could get interesting. idaho requires a title on every trailer, down to a $200 harbor freight pwc trailer. wisconsin doesn't seem to care on some. been a real pita to get the boat trailer titled/plated in wi as it's over some predetermined length that needs registration but with my $3000 enclosed sled trailer, no plate, no title, no bill of sale, hook up and take it. wierd to me....