Re: Proper size
Your trailer is not determined by the size of boat but rather by the weight, sometimes you can have a tandem axle on a 17' boat which would be overkill in almost any case but there are advantages to a tandem.
I quick google of your boat indicates roughly an 1800 lb boat and is well within a single axle trailers capabilities, however if you tow frequently and for long distances a tandem would be a good idea and great piece of mind, tandems also tow better but a properly set up single axle trailer will tow just fine as well, need a little more info from you about the towing you plan to do.
overall size of trailer? your probably looking at a 25'-28' trailer roughly, I typically go a little longer tongue on my trailers because they tow better but I tow 800 miles sometimes so you can see where a trailer that tows great would be nice for me.
