Do you want a single or double axle?
Do you prefer bunks or rollers?
What type of braking do you want? (hydraulic, electric, surge)
Answer those if you can and I am sure we can make educated guesses at least.
In the meantime, I will tell you what we use as one example for a heavy 19.
King
KB3700S
APPROX. BOAT LENGTH RANGE: 18'-20'
LOAD CAPACITY: 3700
APPROX. OVER ALL LENGTH: 22' 11"
APPROX. OVER ALL WIDTH: 102"
WIDTH BETWEEN FENDERS: 80"
BOW EYE TO TRANSOM MIN.: 15' 10"
BOW EYE TO TRANSOM MAX.: 20'
APPROX. WEIGHT: 840 #
TIRE SIZE: ST225/75 15D
TONGUE JACK: 1000 #
NUMBER OF BUNKS: 4-10'
COUPLER SIZE: 2"-CL3
Greg