Another option is contact all the Moomba dealers around you see if they have a customer that keeps there boat in a slip or off trailer storage most of the time and they might be willing to do the same thing.

The good thing about the single axle trailer is the axle is much stronger then the duels. Its rated around 6k where the duel is rated around 3.7k but your right about wanting a duel axle for long pulls. This is exactly why i made sure we got a duel axle trailer because i knew id be putting a lot of miles on my trailer.

Another option but a bit of a stalking option is goto the local Marinas and see what trailers are stored for boats in slips and then track that owner down and proposition them. I know a bit creepy but the worst they will say is F off LOL.