Bigger is better !!
Trust me ! DO it now !!!
Mine is 35 x 60 , 4 bays that are 15 feet wide with 12' ceilings. It is NOT big enough !!!
It was good when I had a 24' Baja . That didn't last long .... Now my 39' cat is 12 feet wide and half of it sticks outside ! Get the doors as tall and wide as you can . You might want to work on top of your boat while it's inside and you will be crawling on your stomach if you don't ! Also you need to be able to open the engine hatches while inside .
If you use role up doors , remember when they are open they take up a lot of head room !
I don't think the 336 that you asked about will fit inside a 40' garage and close the door . You will have 4-5 feet of trailer in front of it and 2-3 feet of drive behind .
Don't forget , your role up doors will not be flush to the outside . I lost another foot when I installed mine , PLUS the 3" ribbs on the inside of the doors !!

So now your garage just went from 40' to 38'7" .....
My next garage will be one bay !
20 feet wide and 90 feet deep !! That way I can back the boat and truck inside and leave it hooked up and still have room left !
