I asked my dad when he was visiting me.
he stated that GM designs its gates form 500lb to 1000lb , and since they have seats the gate rating would follow the standard weight rating as its seats with is 250lb per person. but he did say he didn't think the plast would hold up to that weight easly if it wasn't hallow. he figured that it may that it may have a 500lb rating too but he wouldn't test it. GM has alwat been realy good about making strong gates thats what i love about them. he put a request on it to the GM guys to get that documentaion on it. but he thinks it may just be a supped up truck gate with a nice plastic cover.
he stated that 450lb would be better with the plastic
i will note i've had about 700lb worth of people on it at one time with no problems (its my friend johnny and his wife tina not me). and have move a 400lb fridge in mine now with all the weight on the gate with no problems. i've only seen one gate fail due to weight in my life and it had a 2500lb round bail fall 3ft above it. my grandpa was realy pissed