Shelter king makes a nice carport. Im figuring you are talking about the tarp style ones. The internal structure is heavy duty and the cover material is thick too. I think they offer custom sizing as well. I have mine fo over 5 years now still in good shape and it handles snow pretty well too. Mine is a 12'*20' and was about $550/600 delivered. You can get them where both ends open so if you wanted you could just drive straight through till the boat is in.
you bought the wrong trailer. The tires on the inside with the adjustable height crank then lower it 12"-20" more and your in. I use a trailer with inside wheels all summer long. Both friend have a marina. I move LOTS of boats.
try tempo.com or some thing like that , we use them for the winter months , i have a 20x24x7 for my double garage , take about 2.5 hrs to put up and a little longer to remove
it a big theing here for the winter season