I purchased a sturdy 10 x 20 ft canopy cover to cover my 19 foot Shamrock 183. I easily extended the legs using 10 foot electrical conduit instead of the stock legs giving me 10 foot tall (on the sides) and 14 foot tall in the middle. I staked the top frame down at all four corners and in the middle against high winds. Has been standing over my trailer now since last May.
You can start with a canopy from harbor freight dot com or SHelter Logic
or Norther Tool dot com or any big box store and purchase an additional kit to make it longer to fit your trailer. A great site to purchase additional canopy fittings is
Yuma Bargain Warehouse
This has withstood one heavy snow load already this year.
The only thing that rubs the canopy top is the whip antenna and I have that tied down now. This keeps the sun and rain off the top yet leaves plenty of room for air movement.