I put this DIY Spring assist on My 6.4 x12 Dovetail trailer Today.
Because of Health conditions It was tough for me to lower it or raise it and hurt my Back and Neck to do it.
I bought 4 of the 5/16 Zinc Plated Quick links
8 of the 3/8 Zinc flat washers
And a 2 pack of Dura-Lift 160 LB Extension Garage door Springs
And 4 of the 3/8 eye Zinc Plated Eye bolt with nut
Used a 4 lock washers I had
Drilled 1 hole in the Trailer Frame and 1 Hole in the Loading Gate
Including tax,The Cost was Less than 49 Bucks from Home Depot
I have only tried it with One of the 160 LB springs and it is very easy to start pulling the Loading gate down and dropthe gate when it it is about 8 inches from the Ground.
I can now raise the Loading Gate very easily using only 2 fingers.
And still have 2 of the 5/16 Quick Links left over
And 4 of the 3/8 Flat washers left over
And still have a 160 LB Garage door Extension Spring left over
And still have 2 of the 3/8 Eye bolts Left
So I have enough Left Over to do another spring assist on another Trailer.
A hell of a lot money less than buying a commercially Made Spring assist and took about 30 Minutes from start to finish to do.